VEL A Distance & Displacement & VEL B Speed and Velocity 1. You run from your house to a friend's house that is 3 miles away. You then walk home.

Transcription

1 VEL A Distance & Displacement & VEL B Speed and Velocity 1. You run from your house to a friend's house that is 3 miles away. You then walk home. a. What distance did you travel? b. What was the displacement for the entire trip? 2. Observe the diagram below. A person starts at A, walks along the bold path and finishes at B. Each square is 1 km along its edge. Use the diagram in answering the next two questions. 3. This person walks a distance of km. 4. This person has a displacement of. a. 0 km b. 3 km c. 3 km, E d. 3 km, W e. 5 km f. 5 km, N g. 5 km, S h. 6 km i. 6 km, E j. 6 km, W k. 31 km l. 31 km, E m. 31 km, W n. None of these. 5. A child crawls 12 m South and then 14 m West. Determine their total displacement. (Include a vector diagram) 6 A student goes for a hike and travels 2.4 km North and then 5.2 km West. Determine their total displacement. (Include a vector diagram) Answer to Vel A Dist & Dipl

2 Vel B Speed and Velocity 1. A polar bear walks a distance of 160 meters in 60 seconds. What was its speed? 2. A train travels 120 seconds at a speed of 50 m/s. How far did it go? 3. How long will it take a runner to travel a distance of 1000 m at a speed of 12 m/s? 4. A car travels a distance of 1600 km in 24 hours. What was its speed? 5. A sailboat travels a distance of 600 m in 40 seconds. What speed is it going? 6. What distance will a car traveling at a speed of 50 km/hr cover in 0.25 hr? 7. How long will it take a ball to roll 10 meters along the floor at a speed of 0.5 m/s? Answers to VEL B - Speed and Velocity 1) 2.67 m/s 2) 6000 m 3) 83.3 s 4) 66.7 km/h 5) 15 m/s 6) 12.5 km 7) 20 s ACC D Projectile Motion A ball is launched horizontally from the top of a cliff with an initial velocity of 20 m/s. The trajectory of the ball is shown below. Express your understanding by filling in the blanks.

3 VEL C Motion Graphs 1. The slope of the line on a position vs. time graph reveals information about an object's velocity. The magnitude (numerical value) of the slope is equal to the object's speed and the direction of the slope (upward/+ or downward/- ) is the same as the direction of the velocity vector. Apply this understanding to answer the following questions. a. A horizontal line means. b. A straight diagonal line means. c. A curved line means. d. A gradually sloped line means. e. A steeply sloped line means. 2. The motion of several objects is depicted on the position vs. time graph. Answer the following questions. Each question may have less than one, one, or more than one answer. a. Which object(s) is(are) at rest? b. Which object(s) is(are) accelerating? c. Which object(s) is(are) not moving? d. Which object(s) change(s) its direction? e. Which object is traveling fastest? f. Which moving object is traveling slowest? g. Which object(s) is(are) moving in the same direction as object B? 3. On the graphs below, DRAW TWO LINES to represent the given verbal descriptions; label the lines/curves as A or B. A B Remaining at rest Moving A B Moving slow Moving fast A B Moving in + direction Moving in - direction 4. Use the position-time graphs below to determine the velocity.

4 Answers - VEL C Motion Graphs 1. a. A horizontal line means the velocity is 0 m/s (object is at rest). b. A straight diagonal line means the velocity is constant. c. A curved line means the velocity is changing (acceleration). d. A gradually sloped line means the velocity is small (slow). e. A steeply sloped line means the velocity is large (fast). 2. AE a. Which object(s) is(are) at rest? D b. Which object(s) is(are) accelerating? AE c. Which object(s) is(are) not moving? none d. Which object(s) change(s) its direction? B e. Which object is traveling fastest? D (on average) f. Which moving object is traveling slowest? D g. Which object(s) is(are) moving in the same direction as object B? 3. A Remaining at rest B Moving A (horizontal) A B Moving slow Moving fast B B (more sloped) A A B Moving in + direction Moving in - direction B A 4. Use the position-time graphs below to determine the velocity. v = slope = rise/run = (20 m)/(5.0 s) v = 4 m/s v = slope = rise/run = (20 m)/(5.0 s) v = 4 m/s v = slope = rise/run = (-25 m)/(5.0 s) v = -5 m/s v = slope = rise/run = (-20 m)/(5.0 s) v = -4 m/s

5 ACC A Acceleration and Free-fall The Concept of Acceleration 1. Accelerating objects are objects that are changing their velocity. Name the three controls on an automobile that cause it to accelerate. 2. An object is accelerating if it is moving. Circle all that apply. a. with changing speed b. extremely fast c. with constant velocity d. in a circle e. downward f. none of these 3. If an object is NOT accelerating, then one knows for sure that it is. a. at rest b. moving with a constant speed c. slowing down d. maintaining a constant velocity Acceleration as a Rate Quantity Acceleration is the rate at which an object's velocity changes. The velocity of an object refers to how fast it moves and in what direction. The acceleration of an object refers to how fast an object changes its speed or its direction. Objects with a high acceleration are rapidly changing their speed or their direction. As a rate quantity, acceleration is expressed by the equation: acceleration = Velocity time = v final - voriginal time 4. An object with an acceleration of 10 m/s 2 will. Circle all that apply. a. move 10 meters in 1 second b. change its velocity by 10 m/s in 1 s c. move 100 meters in 10 seconds d. have a velocity of 100 m/s after 10 s 5. Ima Speedin puts the pedal to the metal and increases her speed as follows: 0 mi/hr at 0 seconds; 10 mi/hr at 1 second; 20 mi/hr at 2 seconds; 30 mi/hr at 3 seconds; and 40 mi/hr at 4 seconds. What is the acceleration of Ima's car? 6. Mr. Henderson's (imaginary) Porsche accelerates from 0 to 60 mi/hr in 4 seconds. Its acceleration is. a. 60 mi/hr b. 15 m/s/s c. 15 mi/hr/s d. -15 mi/hr/s e. none of these 7. A car speeds up from rest to +16 m/s in 4 s. Calculate the acceleration. 8. A car slows down from +32 m/s to +8 m/s in 4 s. Calculate the acceleration. 9. In the absence of air friction all objects accelerate. A. at different rates bigger objects have more acceleration B. the same rate all objects have the same acceleration C. at different rates smaller objects have more acceleration 10. Acceleration due to gravity near the surface of Earth is meaning that. A. Every second you fall, you travel 9.8 meters. B. Every meter you fall takes 9.8 seconds C. Every 9.8 meters takes a second squared D. Every second you fall your velocity increases by 9.8 m/s

6 Answers ACC A - Acceleration and Free fall The Concept of Acceleration 1. Acceleration is a change in velocity - either in the speed or in the direction. The brake pedal and gas pedal cause speed changes. The steering wheel causes direction changes. 2. An object is accelerating if it is moving. Circle all that apply. a. with changing speed b. extremely fast c. with constant velocity d. in a circle e. downward f. none of these Accelerating objects are changing their velocity. A velocity is a speed with a direction. An object with a changing velocity can be changing its speed (choice a) and/or changing its direction (choice d). 3. If an object is NOT accelerating, then one knows for sure that it is. a. at rest b. moving with a constant speed c. slowing down d. maintaining a constant velocity If an object is not accelerating, then it is not changing its velocity. The velocity is constant. A velocity is a speed with a direction; so if it has a constant velocity, then it also has a constant speed and direction. Acceleration as a Rate Quantity 4. An object with an acceleration of 10 m/s 2 will. Circle all that apply. a. move 10 meters in 1 second b. change its velocity by 10 m/s in 1 s c. move 100 meters in 10 seconds d. have a velocity of 100 m/s after 10 s 5. Ima Speedin puts the pedal to the metal and increases her speed as follows: 0 mi/hr at 0 seconds; 10 mi/hr at 1 second; 20 mi/hr at 2 seconds; 30 mi/hr at 3 seconds; and 40 mi/hr at 4 seconds. What is the acceleration of Ima's car? Ima's acceleration is 10 mi/hr/s because her speed changes by 10 mi/hr each second. 6. Mr. Henderson's (imaginary) Porsche accelerates from 0 to 60 mi/hr in 4 seconds. Its acceleration is 15 mi/hr/s. a. 60 mi/hr b. 15 m/s/s c. 15 mi/hr/s d. -15 mi/hr/s e. none of these 7. A car speeds up from rest to +16 m/s in 4 s. Calculate the acceleration. a = velocity / time = (16 m/s - 0 m/s)/(4 s) = (16 m/s) / (4 s) = 4 m/s 2 8. A car slows down from +32 m/s to +8 m/s in 4 s. Calculate the acceleration. a = velocity / time = (8 m/s - 32 m/s)/(4 s) = (-24 m/s) / (4 s) = - 6 m/s 2 9. In the absence of air friction all objects accelerate. A. at different rates bigger objects have more acceleration B. the same rate all objects have the same acceleration C. at different rates smaller objects have more acceleration 10. Acceleration due to gravity near the surface of Earth is meaning that. A. Every second you fall, you travel 9.8 meters. B. Every meter you fall takes 9.8 seconds C. Every 9.8 meters takes a second squared D. Every second you fall your velocity increases by 9.8 m/s

7 ACC B Motion Graphs Review: Categorize the following motions as being either examples of + or - acceleration. a. Moving in the + direction and speeding up (getting faster) b. Moving in the + direction and slowing down (getting slower) c. Moving in the - direction and speeding up (getting faster) d. Moving in the - direction and slowing down (getting slower) 1. Consider the following graph of a car in motion. Use the graph to answer the questions. a. Describe the motion of the car during each of the two parts of its motion. 0-5 s: 5-15 s: b. Determine the acceleration of the car during each of the two parts of its motion. 0-5 s 5-15 s 2. Consider the following graph of a car in motion. Use the graph to answer the questions. a. Describe the motion of the car during each of the four parts of its motion s: s: s: s: b. Determine the acceleration of the car during each of the four parts of its motion s s s s 3. The slope of the line on a velocity vs. time graph reveals information about an object's acceleration. Furthermore, the area under the line is equal to the object's displacement. Apply this understanding to answer the following questions. a. A horizontal line means. b. A straight diagonal line means. c. A gradually sloped line means. d. A steeply sloped line means. 4. The motion of several objects is depicted by a velocity vs. time graph. Answer the following questions. Each question may have less than one, one, or more than one answer. a. Which object(s) is(are) at rest? b. Which object(s) is(are) accelerating? c. Which object(s) is(are) not moving? d. Which object(s) change(s) its direction? e. Which accelerating object has the smallest acceleration? f. Which object has the greatest acceleration? g. Which object(s) is(are) moving in the same direction as object E?

8 5. On the graphs below, draw two lines/curves to represent the given verbal descriptions; label the lines/curves as A or B. A Moving at constant speed A Move in + dirn; speed up A Move in - dirn; speed up B Accelerating B Move in + dirn; slow dn B Move in - dirn; slow dn 6. For each type of accelerated motion, construct the appropriate shape of a position-time graph. Moving with a + velocity and a + acceleration Moving with a + velocity and a - acceleration Moving with a - velocity and a + acceleration Moving with a - velocity and a - acceleration 7. Use the velocity-time graphs below to determine the acceleration. Graphing Summary Answers ACC B Motion Graphs

9 Review: Categorize the following motions as being either examples of + or - acceleration. a. Moving in the + direction and speeding up (getting faster) positive b. Moving in the + direction and slowing down (getting slower) negative c. Moving in the - direction and speeding up (getting faster) negative d. Moving in the - direction and slowing down (getting slower) positive 1. Consider the following graph of a car in motion. Use the graph to answer the questions. a. Describe the motion of the car during each of the two parts of its motion. 0-5 s: The car is moving in the positive direction and speeding up (accelerating) s: The car is moving in the positive direction at a constant velocity (a=0 m/s/s). b. 0-5 s 5-15 s a = slope = rise/run a = slope = rise/run a = (20 m/s)/(5 s) a = (0 m/s)/(10 s) a = 4 m/s/s a = 0 m/s/s 2. Consider the following graph of a car in motion. Use the graph to answer the questions. Describe the motion of the car during each of the four parts of its motion s: The car is moving in the positive direction at a constant velocity (a=0 m/s/s) s: The car is moving in the positive direction and speeding up (accelerating) s: The car is moving in the positive direction at a constant velocity (a=0 m/s/s) s: The car is moving in the positive direction and slowing down. b s s s s a= slope=rise/run a= slope=rise/run a= slope=rise/run a= slope=rise/run a=(0 m/s)/(10 s) a=(5 m/s)/(10 s) a=(0 m/s)/(10 s) a=(-15 m/s)/(5 s) a=0 m/s/s a=0.5 m/s/s a=0 m/s/s a=-3 m/s 3. a. A horizontal line means constant velocity (a = 0 m/s/s). b. A straight diagonal line means accelerating object. c. A gradually sloped line means small acceleration. d. A steeply sloped line means large acceleration a. Which object(s) is(are) at rest? BCD b. Which object(s) is(are) accelerating? --- c. Which object(s) is(are) not moving? BC d. Which object(s) change(s) its direction? B e. Which accelerating object has the smallest acceler'n? C f. Which object has the greatest acceleration? D (sort of BC) g. Which object(s) is(are) moving in the same direction as object E?

10 5. A Moving at constant speed B Accelerating A B Move in + dirn; speed up Move in + dirn; slow dn A B Move in - dirn; speed up Move in - dirn; slow dn B A B A B A 6. Moving with a + velocity and a + acceleration Moving with a + velocity and a - acceleration positive slope (getting steeper) Moving with a - velocity and a + acceleration positive slope Moving with a - velocity and a - acceleration Negative slope (getting flatter) 7. Use the velocity-time graphs below to determine the acceleration. PSYW Negative slope (getting steeper) a = v/t = (32 m/s - 4 m/s)/(8.0 s) a = 3.5 m/s/s a = v/t = (8 m/s - 32 m/s)/(12.0 s) a = -2.0 m/s/s Graphing Summary

11 ACC C Kinematic Equations 1. An airplane accelerates down a run-way at 3.20 m/s 2 for 32.8 s until is finally lifts off the ground. Determine the distance traveled before take-off. 2. A race car accelerates uniformly from 18.5 m/s to 46.1 m/s in 2.47 seconds. Determine the acceleration of the car and the distance traveled. 3. A feather is dropped on the moon from a height of 1.40 meters. The acceleration of gravity on the moon is 1.67 m/s 2. Determine the time for the feather to fall to the surface of the moon. 4. A bullet leaves a rifle with a muzzle velocity of 521 m/s. While accelerating through the barrel of the rifle, the bullet moves a distance of m. Determine the acceleration of the bullet (assume a uniform acceleration). 5. An engineer is designing a runway for an airport. Several planes will use the runway and the engineer must design it so that it is long enough for the largest planes to become airborne before the runway ends. If the largest plane accelerates at 3.30 m/s 2 and has a takeoff speed of 88.0 m/s, then what is the minimum allowed length for the runway? DYN A Inertia 2. The amount of inertia possessed by an object is dependent solely upon its. 6. Inertia can best be described as. a. the force that keeps moving objects moving and stationary objects at rest. b. the willingness of an object to eventually lose its motion c. the force that causes all objects to stop d. the tendency of any object to resist change and keep doing whatever it's doing 7. Mass and velocity values for a variety of objects are listed below. Rank the objects from smallest to greatest inertia. < < <

12 Answer to ACC C Kinematic Equations 1. An airplane accelerates down a run-way at 3.20 m/s 2 for 32.8 s until is finally lifts off the ground. Determine the distance traveled before take-off. Given: a = 3.20 m/s 2 t = 32.8 s v o = 0 m/s Unknown: d =??? Relevant Equation: d = v o t + ½ a t 2 Solution: d= (0 m/s) (32.8 s) + ½ (3.20 m/s 2 ) (32.8 s) 2 d= 0 m m Answer: 1721 m = 1720 m (3 sig figs) 2. A race car accelerates uniformly from 18.5 m/s to 46.1 m/s in 2.47 seconds. Determine the acceleration of the car. Given: v o=18.5 m/s v f=46.1 m/s t=2.47 s Unknown: a =??? Relevant Equation: d = ½ (v o + v f) t Solution: d = ½ (18.5 m/s m/s) (2.47 s) d = ½ (64.6 m/s) (2.47 s) Answer: 79.8 m 3. A feather is dropped on the moon from a height of 1.40 meters. The acceleration of gravity on the moon is 1.67 m/s 2. Determine the time for the feather to fall to the surface of the moon. Given: v o=0 m/s d=1.40 m a=1.67 m/s 2 Unknown: t=??? Relevant Equation: d = v o t + ½ a t 2 Solution: 1.40 m = (0 m/s) (t) + ½ (1.67 m/s 2 ) t m = (0.835 m/s 2 ) t 2 t 2 = (1.40 m) / (0.835 m/s 2 ) t = SQRT( s 2 ) (SQRT = square root) Answer: 1.29 s 4. A bullet leaves a rifle with a muzzle velocity of 521 m/s. While accelerating through the barrel of the rifle, the bullet moves a distance of m. Determine the acceleration of the bullet (assume a uniform acceleration). Given: v o=0 m/s v f=521 m/s d=0.840 m Unknown: a=??? Relevant Equation: v 2 f = v 2 o + 2 a d Solution: (521 m/s) 2 = (0 m/s) a (0.840 m) m 2 /s 2 = (1.680 m) a a = ( m 2 /s 2 ) / (1.680 m) Answer: 1.62 x 10 5 m/s 2 (3 sig figs) 5. An engineer is designing a runway for an airport. Several planes will use the runway and the engineer must design it so that it is long enough for the largest planes to become airborne before the runway ends. If the largest plane accelerates at 3.30 m/s 2 and has a takeoff speed of 88.0 m/s, then what is the minimum allowed length for the runway? Given: v o=0 m/s a=3.30 m/s 2 v f=88.0 m/s Unknown: DDD=??? Relevant Equation: v f 2 = v o a d Solution: (88.0 m/s) 2 = (0 m/s) (3.30 m/s 2 ) d d = (7744 m 2 /s 2 ) / (6.60 m/s 2 ) Answer: 1173 m = 1170 m (3 sig figs) Answers DYN A Inertia 2. The amount of inertia possessed by an object is dependent solely upon its mass. 6. Inertia can best be described as D. a. the force that keeps moving objects moving and stationary objects at rest. b. the willingness of an object to eventually lose its motion c. the force that causes all objects to stop d. the tendency of any object to resist change and keep doing whatever it's doing 7. Mass and velocity values for a variety of objects are listed below. Rank the objects from smallest to greatest inertia. C < D < A < B Objects with the least mass have the least amount of inertia; objects with the most mass have the greatest amount of inertia. The velocity or speed of the object has nothing to do with inertia.

13 DYN C Newton s 2 nd Law 5. A 2.0-N force is applied to a 1.0 kg book in order to move it across a desk with an acceleration of 0.5 m/sec 2. Consider frictional forces. Neglect air resistance. Diagram the forces acting on the book. FBD: Fx = Fy = ax = ay = 6. A 1.5-N force is applied to a 1.0 kg book in order to move it across a desk at constant velocity. Consider frictional forces. Neglect air resistance. Diagram the forces acting on the book. FBD: Fx = Fy = ax = ay = 7. A 70.0-kg skydiver is descending with a constant velocity. Consider air resistance. Diagram the forces acting upon the skydiver. FBD: Fx = Fy = ax = ay = 8. A 30-N force is applied to drag a 20-kg sled across loosely packed snow with an acceleration of 1.0 m/s 2. Diagram the forces acting upon the sled. FBD: Fx = Fy = ax = ay = 9. An 800-kg car is coasting to the right with a leftward acceleration of 1 m/s 2. Diagram the forces acting upon the car. FBD: Fx = Fy = ax = ay =

14 Answers DYNC Newton s 2 nd Law 5. A 2.0-N force is applied to a 1.0 kg book in order to move it across a desk with an acceleration of 0.5 m/sec 2. Consider frictional forces. Neglect air resistance. Diagram the forces acting on the book. F frict = 1.5 N FBD: F norm = 9.8 N F grav = 9.8 N F app = 2.0 N Fx = 0.50 N, right ax = 0.5 m/s 2, right Fy = 0 N ay = 0 m/s 2 6. A 1.5-N force is applied to a 1.0 kg book in order to move it across a desk at constant velocity. Consider frictional forces. Neglect air resistance. Diagram the forces acting on the book. FBD: Fx = 0 N Fy = 0 N F frict = 2.0 N F norm = 9.8 N F app = 2.0 N ax = 0 m/s 2 ay = 0 m/s 2 F grav = 9.8 N 7. A 70.0-kg skydiver is descending with a constant velocity. Consider air resistance. Diagram the forces acting upon the skydiver. FBD: F air = 686 N Fx = 0 N ax = 0 m/s 2 Fy = 0 N ay = 0 m/s 2 F grav = 686 N 8. A 30-N force is applied to drag a 20-kg sled across loosely packed snow with an acceleration of 1.0 m/s 2. Diagram the forces acting upon the sled. FBD: Fx = 20.0 N, right Fy = 0 N F frict = 20.0 N F norm = 196 N F app = 30.0 N ax = 1.0 m/s 2 ay = 0 m/s 2 F grav = 196 N 9. An 800-kg car is coasting to the right with a leftward acceleration of 1 m/s 2. Diagram the forces acting upon the car. FBD: Fx = 800 N, left Fy = 0 N F air = 800 N F norm = 7840 N ax = 1.0 m/s 2, left ay = 0 m/s 2 F grav = 7840 N

15 DYN D Newtons 3 rd Law 3. TRUE or FALSE: As you sit in your seat in the physics classroom, the Earth pulls down upon your body with a gravitational force; the reaction force is the chair pushing upwards on your body with an equal magnitude. If False, correct the answer. 4. Shirley Bored sits in her seat in the English classroom. The Earth pulls down on Shirley's body with a gravitational force of 600 N. Describe the reaction force of the force of gravity acting upon Shirley. 5. Use Newton's third law (law of action-reaction) and Newton's second law (law of acceleration: a = Fnet/m) to complete the following statements by filling in the blanks. a. A bullet is loaded in a rifle and the trigger is pulled. The force experienced by the bullet is (less than, equal to, greater than) the force experienced by the rifle. The resulting acceleration of the bullet is (less than, equal to, greater than) the resulting acceleration of the rifle. b. A bug crashes into a high-speed bus. The force experienced by the bug is (less than, equal to, greater than) the force experienced by the bus. The resulting acceleration of the bug is (less than, equal to, greater than) the resulting acceleration of the bus. c. A massive linebacker collides with a smaller halfback at midfield. The force experienced by the linebacker is (less than, equal to, greater than) the force experienced by the halfback. The resulting acceleration of the linebacker is (less than, equal to, greater than) the resulting acceleration of the halfback. d. The 10-ball collides with the 14-ball on the billiards table (assume equal mass balls). The force experienced by the 10-ball is (less than, equal to, greater than) the force experienced by the 14-ball. The resulting acceleration of the 10-ball is (less than, equal to, greater than) the resulting acceleration of the 14- ball.

16 Answers DYN D Newton s 3 rd Law 3. TRUE or FALSE: As you sit in your seat in the physics classroom, the Earth pulls down upon your body with a gravitational force; the reaction force is the chair pushing upwards on your body with an equal magnitude. If False, correct the answer. The reaction force to the Earth pulling down on your body is the force of your body pulling up on the Earth. 4. Shirley Bored sits in her seat in the English classroom. The Earth pulls down on Shirley's body with a gravitational force of 600 N. Describe the reaction force of the force of gravity acting upon Shirley. Shirley's body pulls upward on the Earth with 600 N of force. Gravitational force, like all forces, results from a mutual interaction. In the case of gravity, it is the mutual attraction of two objects for one another. Not only does the Earth attract Shirley's mass, Shirley attracts the Earth's mass. 5. Use Newton's third law (law of action-reaction) and Newton's second law (law of acceleration: a = Fnet/m) to complete the following statements by filling in the blanks. a. A bullet is loaded in a rifle and the trigger is pulled. The force experienced by the bullet is equal to (less than, equal to, greater than) the force experienced by the rifle. The resulting acceleration of the bullet is greater than (less than, equal to, greater than) the resulting acceleration of the rifle. b. A bug crashes into a high-speed bus. The force experienced by the bug is equal to (less than, equal to, greater than) the force experienced by the bus. The resulting acceleration of the bug is greater than (less than, equal to, greater than) the resulting acceleration of the bus. c. A massive linebacker collides with a smaller halfback at midfield. The force experienced by the linebacker is equal to (less than, equal to, greater than) the force experienced by the halfback. The resulting acceleration of the linebacker is less than (less than, equal to, greater than) the resulting acceleration of the halfback. d. The 10-ball collides with the 14-ball on the billiards table (assume equal mass balls). The force experienced by the 10-ball is equal to (less than, equal to, greater than) the force experienced by the 14-ball. The resulting acceleration of the 10-ball is equal to (less than, equal to, greater than) the resulting acceleration of the 14-ball.

17 DYN F Friction Review 1. What is the formula for calculating the force of gravity? 2. What is a normal force? What does normal force mean? 3. A textbook is at rest on a table. There are only two forces acting on the book; the force of gravity and the normal force. Draw a free-body diagram of the textbook at rest on the table with the two forces present. 4. True or False? Explain why The force of gravity on the textbook is equal to the normal force. 5. True or False? Explain why Weight and force of gravity are the same thing. Conceptual 1. True or False? Explain why Friction is a force opposing motion; therefore friction is always in the opposite direction of the motion. 2. True or False? Explain why Kinetic Friction and Static Friction is the same thing. 3. True or False? Explain why Kinetic Friction is greater than Static Friction because objects create more friction when they are moving. 4. True or False? Explain why The greater the coefficient of friction, the greater the force of friction a surface can create therefore resulting in more friction being present as an object moves across the surface. Computational 1. The coefficient of kinetic friction between an object and the surface upon which it is sliding is The mass of the object is 16kg. What is the force of friction? 2. The coefficient of kinetic friction between an object and the surface upon which it is sliding is The mass of the object is 8.0 kg. What is the force of friction? 3. The force of friction between an object and the surface upon which it is sliding is 46N and the coefficient of friction between them is What is the weight of the object? 4. The force of friction between an object and the surface upon which it is sliding is 360N. The mass of the object is 95kg. What is the coefficient of kinetic friction? 5. The force of friction between an object and the surface upon which it is sliding is 126 N and the coefficient of friction between them is What is the mass of the object?

18 DYN F Friction Answers 1. What is the formula for calculating the force of gravity? The formula for the force of gravity is : where g, or acceleration due to gravity equals 9.8 m/s 2 2. What is a normal force? What does normal force mean? Normal force is a force a surface pushing on an object. Most commonly, normal force is used to describe the force a table or a desk pushed up on an object at rest on the table or desk. Normal force is not always straigt up. It is sometimes at an angle when the surface is slanted or sloped. 3. A textbook is at rest on a table. There are only two forces acting on the book; the force of gravity and the normal force. Draw a free-body diagram of the textbook at rest on the table with the two forces present. Normal Force Force of gravity 4. True or False? Explain why The force of gravity on the textbook is equal to the normal force. TRUE! The force of gravity going down is equal to the normal force going up because the textbook is not moving up or down and there are no other forces acting on the book in the up or down direction. Therefore the forces going up and going down must be balanced or equal. 5. True or False? Explain why Weight and force of gravity are the same thing. TRUE! The force of gravity is called your weight textbook Conceptual 1. True or False? Explain why Friction is a force opposing motion; therefore friction is always in the opposite direction of the motion. TRUE! Friction opposes motion therefore friction is in the opposite direction of motion. If an object is moving to the right, then friction is to the left. If a car is moving to the left, and slowing down, it is still moving to the left and in this case, friction is to the right. 2. True or False? Explain why Kinetic Friction and Static Friction is the same thing. FALSE! Kinetic friction is the friction that exists between an object and a surface when the object is moving. Static friction is the friction that exists between an object and a surface when the object is not moving, or at rest. 3. True or False? Explain why Kinetic Friction is greater than Static Friction because objects create more friction when they are moving. FALSE! Kinetic friction is less than Static Friction. Think of it in terms of Newton s 1 st Law. An object at rest, wants to stay at rest. Therefore an object at rest requires more force to begin motion. The object is at rest and wants to stay at rest; therefore it has more friction than on object in motion. Again, think about in terms of Newton s 1st Law. An object in motion wants to stay in motion, therefore it requires less force to keep it moving, it has less opposition to a force that wants to keep it moving, and therefore it creates less friction. 4. True or False? Explain why The greater the coefficient of friction, the greater the force of friction a surface can create therefore resulting in more friction being present as an object moves across the surface. TRUE! The formula is: or where the symbol stands for coefficient of friction. Therefore, the greater that number for, the greater the force of friction will be. For example, a piece of steel on top of another piece of steel has a coefficient of friction of about 0.7. The coefficient of friction between two pieces of ice is Also, the coefficient of STATIC friction between two materials is greater than the coefficient of KINETIC friction between the same two materials. or Answers Computational 1)23.52 N 2)7.84 N 3) N 4) ) 64.3 kg

19 UCM A Velocity

20 Computational UCM A Velocity Answers

21 UCM B Acceleration Computational UCM B Accelerations

22 Answers to UCM B Acceleration Computational 1 2,500 m/s/s m/s/s m/s/s m/s/s 9. TOP: 12 m/s/s, down BOTTOM: 32 m/s/s 10.

23 Conceptual UCM C Force Computational

24 Conceptual Answer to UCM- C Force Computational 10) 21, N