For each of the following questions, give clear and complete evidence for your choice in the space provided.

Transcription

1 Name (printed) First Day Stamp For each of the following questions, give clear and complete evidence for your choice in the space provided. 1. An astronomer observes that a certain heavenly body is moving at constant speed in a straight line. He or she can conclude from this that the unbalanced force acting on the body is: a. zero c. constant but not zero b. at right angles to the path of the body d. in the same direction as the body s motion 2. A block is dragged without acceleration in a straight line path across a level surface by a force of 6 N. What is the force of friction between the block and the surface? a. less than 6 N b. 6 N c. more than 6 N 3. Two people are balanced on a see-saw. If one person leans toward the center of the see-saw, that person s end of the see-saw will a. rise. b. fall. c. stay at the same level. 4. The 40-kg woman stands at the end of a 4.0 m long uniform plank. If the maximum overhang of the plank is 1.0 meter, what is the mass of the plank? a. 10 kg b kg c. 40 kg d. 120 kg 5. In the diagram to the right, the board is balanced as shown. If the board were not moved, but the two masses were moved twice as far from the point of rotation, what would happen to the board s balance? a. The board would stay balanced. b. The left side of the board would rise. c. The right side of the board would rise. 2 kg 1 kg board center of mass 1

2 6. As a skydiver falls from an airplane through the air (before terminal velocity), what is true about her speed and acceleration? a. speed increasing, acceleration decreasing d. speed decreasing, acceleration decreasing b. speed increasing, acceleration increasing e. speed increasing, acceleration constant c. speed decreasing, acceleration increasing f. speed decreasing, acceleration constant 7. A 500 N parachutist opens his chute and experiences an air resistance force of 800 N. The net force on the parachutist is: a. 300 N down b. 500 N down c. 800 N down d. 300 N up e. 500 N up 8. The maximum acceleration of a car while towing a second car twice its mass, compared to no towing, is a. one-half. b. one-third. c. one-fourth. d. the same. 9. A bug and a car windshield have a head-on collision. If the mass of the car is 10 7 greater than the mass of the bug, how does the force acting on the bug compare with the force acting on the car? a. The force acting on the bug is 10 7 times greater than the force acting on the car. b. The forces acting on both the bug and the car are identical. c. The force acting on the car is 10 7 times greater than the force acting on the bug. 10. In the previous question, how does the acceleration of the bug compare with the acceleration of the car? a. The acceleration acting of bug is 10 7 times greater than the acceleration of the car. b. The accelerations of both the bug and the car are identical. c. The acceleration of the car is 10 7 times greater than the acceleration of the bug. 11. An archer shoots an arrow. Consider the action force to be the bowstring acting forward on the arrow. Then the reaction force is... a. the bowstring acting backwards on the arrow c. the arrow acting backwards on the bowstring b. the arrow acting forward on the bowstring d. none of these 2 Move ahead 100% CORRECT

3 LAB CALCULATING FRICTION PRE-LAB PROBLEM 1. a. In the diagram to the right, the coefficient of kinetic friction between the 10-kg block and the table is What is the acceleration of the blocks? 10 kg 5 kg b. What would the coefficient of kinetic friction have to be in order for the blocks to accelerate at 2.5 m/s 2? PURPOSE To use Newton s Second Law to calculate and use the coefficient of kinetic (sliding) friction. PROCEDURE (PART 1) 1. Set up your station as shown below. Photogates Friction block and cart 2. Place the friction block on the wood side and hang 300 grams of mass on the string (you ll need to use more than one mass hanger). 3. Measure the time for the friction block and cart to move between the two photogates. Do this five times. Don t worry as much about getting good clustering this time. It won t be as easy. 3

4 DATA 1. Distance between photogates: Time (s) 2. Average time: QUESTIONS/CALCULATIONS (SHOW ALL WORK) 1. Calculate the acceleration of the system. 2. Draw a free body diagram for the cart on the track and then calculate the force of friction acting on the cart. 3. Measure the actual force of friction by using a spring scale while pulling the cart at a constant speed. Determine the percentage error between the actual and calculated forces of friction. 4. Calculate the coefficient due to friction between wood and aluminum using the calculated force of friction. 4

5 PROCEDURE (PART 2) 1. Add 100 grams of mass to the cart. DATA 2. Measure the new time for the friction block and cart to move between the two photogates. Do this five times. 1. Distance between photogates: Time (s) 2. Average time: QUESTIONS/CALCULATIONS (SHOW ALL WORK) 1. Calculate the acceleration of the system using the data above. 2. Use Newton s 2 nd Law to calculate what the acceleration should be under the new conditions (show your steps sequentially and neatly here). 5 Move ahead 100% CORRECT

6 QUESTIONS AND PROBLEMS FRICTION 1. a. In the diagram to the right, the 10-kg block moves from rest to 1.5 m/s over What is the coefficient of kinetic friction between the 10-kg block and the table? 10 kg 5 kg b. What would be the acceleration of the 5 kg block if the 10 kg block were reduced to 8.0 kg? 2. What is the coefficient of kinetic friction between a 7.0-kg brick and a wooden table if 64 N of force is causes it to accelerate at 2.5 m/s 2? (Hint: Find the force of friction first) 3. A 10-kg box is given a push across the floor. Right after the push, it is moving at 4.0 m/s. If the coefficient of friction is 0.20, how far will it go before it stops? 4. If you pushed on the box in the previous problem with 22-N of force, how long would it take you to get it up to 3.0 m/s? 6

7 5. Police can look at skid marks on roads to estimate the speed of the car that left the marks. If a 1,000 kg car left an 80-m skid mark while stopping, how fast was it going when it started to skid? (Assume the coefficient of friction is 0.80.) 6. A 5.00-kg cat is hanging on a tablecloth, pulling an 11-kg fishbowl to the edge. The coefficient of friction between the tablecloth and the table is If the fishbowl is originally 0.90 m from the edge of the table, how long does it take the cat to pull it off the table? 7 A fast 200-kg racecar is trying to slow down as quickly as possible and lets out a parachute that causes an air resistance of 4,000 N. The driver also locks up the brakes, causing friction with the pavement. The coefficient of kinetic friction is If the car is originally moving at 100 m/s, how much distance will it need to stop? 8. In the situation to the right, the coefficient of friction between the kg block and the table is Find acceleration of this block kg 10.0 kg 25.0 kg 7 Move ahead 100% CORRECT

8 LABETTE CENTRIPETAL FORCE INTRODUCTION In this labette a rubber stopper is attached to a hanging mass by means of a long string, threaded through a plastic tube. If you swing the stopper faster and faster, the hanging mass begins to rise. You kind of get a feel for how fast to swing it so that the hanging mass is just suspended, neither moving up nor down. Remember, I said that there is always an agent of centripetal force. That means there must be some physical force pulling inward on the stopper to move it in a circle. You don t have to think too hard to realize that that force is simply the weight of the hanging mass. Your goal is to use the ideas of uniform circular motion to calculate the mass of the rubber stopper. PROCEDURE (PART 1) 1. Set up your apparatus as shown to the right. 2. Choose and measure a convenient radius R at which to swing the rubber stopper. Measure the radius to the center of the stopper. - Use a piece of tape on the string a bit below the plastic tube to help keep the radius constant (but don t let it touch the bottom of the tube). - Don t let any part of your body touch the string or the tape. 3. Use a stopwatch to measure the time for the stopper to go through 30 revolutions. Do this five times with both partners taking turns swinging the stopper. DATA Hanging mass: kg Radius: m Time for 30 revolutions (s) Average time for 30 revolutions: QUESTIONS/CALCULATIONS (SHOW ALL WORK) 1. Calculate the weight of the hanging mass. Period: 2. The weight you calculated in the last question provides the centripetal force to move the rubber stopper in a circle. Use this idea to calculate the mass, in grams, of the rubber stopper. Predicted Mass: Actual Mass: Percent Error: 8

9 PROCEDURE (PART 2) Obtain a mystery mass from me with which to replace the hanging mass. Use the space below to neatly provide all data (using a different radius) and calculations that will lead to the amount of the mystery mass (in grams). Charlotte Simmonds (class of 2006) whirls a rubber stopper in a circle. The stopper is connected to a string, threaded through a glass tube, and attached at the other end to a hanging mass. The weight of the hanging mass provides the centripetal force necessary to keep the stopper moving in a circle. Predicted Mass: Actual Mass: Percent Error: 9 Move ahead 100% CORRECT

10 QUESTIONS AND PROBLEMS UNIFORM CIRCULAR MOTION For questions 3 and 4, give clear and complete evidence for your choice in the space provided. 1. A child rides on a merry-go-round moving at constant speed. Which of the following statements about the child s motion is true? a. Velocity, acceleration, and force are all in the same direction. b. Velocity and acceleration are in the same direction. c. Velocity and force are in the same direction. d. Acceleration and force are in the same direction. 2. A car is traveling in a circular path at constant speed. a. there is a net force on the car directed toward the center of the circle b. there is a net force on the car directed upwards to counter gravity c. there is a net force on the car in the direction the car is traveling in d. there is no net force on the car because the car is not accelerating 3. A car moves at constant speed around a circular curve. Compared to the centripetal force acting on it in this curve, F c what centripetal force will be acting on it if it moves around a curve with half the radius but at twice the speed? F c a. 2 b. F c c. 2F c d. 4F c e. 8F c 4. A trapeze artist is hanging upside down on the bar and holding onto his partner with his dangling hands. Now if they begin to swing back and forth, the amount of force between the two partners: a. decreases b. increases c. stays the same as when they were motionless Do the following questions and problems from the Giancoli book in the space provided on the following two pages. Pages Question 1; Problems 1, 5, 6, 8, 9, 12 10

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12 QUESTIONS AND PROBLEMS THE UNIVERSAL LAW OF GRAVITY For each of the following questions, give clear and complete evidence for your choice in the space provided. 1. The diagram to the right shows two masses, m, separated by a distance, d. m m With these two masses separated at this distance, the gravitational force d between them is 32 N. Use this information and the relationships given in Newton s Law of Gravitation to predict the gravitational force in the situations below. Explain your rationale in each case. a. b. 2m d m c. 2m m d 2m 2d m d. 2m 2d m e. 2m 2m 2. An asteroid exerts a 360-N gravitational force on a nearby spacecraft. If the spacecraft moves to a point three times closer to the center of the asteroid, the force will be a. 40 N b. 120 N c. 1,080N d. 3,240 N 3. A woman who normally weighs 400 N stands on top of a very tall ladder so she is one Earth radius above the Earth s surface. How much would she weigh there? a. 0 b. 100 N c. 200 N d. 400 N 4. If the Earth s mass doubled, but its radius stayed the same, by what factor would your weight change? 1 1 a. b. c. 1 d. 2 e If the Earth s mass stayed the same, but its radius doubled, by what factor would your weight change? 1 1 a. b. c. 1 d. 2 e

13 Do the following problems from the Giancoli book in the space provided on the following two pages. Pages Problems 28, 30, 31, 32, 38, 41 13

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15 QUESTIONS AND PROBLEMS SATELLITES For questions 5 and 6, give clear and complete evidence for your choice in the space provided. 1. What keeps a satellite up? a. Its fuel source c. The fact that it doesn t fall faster than the Earth s curvature b. The loss of gravitational attraction d. The Sun s gravitational pull balances that of the Earth 2. Why are the astronauts weightless? a. Because they are freefalling c. Because they are so far from the pull of the Earth s gravity b. They aren t; they just weigh less d. They actually weigh exactly the same as on the Earth 3. Passengers in a high-flying jumbo jet feel their normal weight in flight, while passengers in the orbiting space shuttle do not. This is because passengers in the space shuttle are a. beyond the main pull of Earth s gravity. d. all of these. b. above the Earth s atmosphere. e. none of these. c. without support forces. 4. Dark matter is theorized to exist because: a. Earth satellites move faster than expected. b. Earth satellites move slower than expected. c. speeds of some stars in galaxies move faster than expected. d. speeds of some stars in galaxies move slower than expected. 5. Two satellites are orbiting a planet, one twice as far from the planet s center as the other. How fast does the more distant satellite move compared to the closer one? a. Half the speed c. Twice the speed b. Slower, but not half the speed d. Faster, but not twice the speed 6. Two satellites are orbiting a planet and one of the satellites is twice the mass of the other satellite. Which of the following is true about the more massive satellite? a. Its altitude must be different from the less massive one. b. Its altitude may be different from the less massive one. c. Its altitude can t be different from the less massive one. Do the following problems from the Giancoli book in the space provided on the following two pages. Pages Problems 43, 48, 60, 62, 88 15

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