Impulse & Linear Momentum

Transcription

1 Name: Per: Date: Los Altos High School Physics Impulse & Linear Momentum r F ave t r = P r r P ox = P fx r r P o = P f r r P oy = P fy r r P = mv Mr. Randall Room 705 adam.randall@mvla.net

2 Impulse & Momentum Unit Objectives and Assignments By the end of this unit, students will be able to: I. Understand impulse and linear momentum so they can: a) Relate mass, velocity, and linear momentum for a moving body, and calculate the total linear momentum for one or two body systems. b) Relate impulse to the change in linear momentum and the average force acting on a body. c) Define impulse and apply the relation between impulse and momentum. d) Determine the impulse given to an object. e) Use the area under Force vs. Time graphs to solve problems about momentum. II. Understand linear momentum conservation so they can: a) State conservation of momentum laws and the conditions required for it. b) Relate Newton s 3 rd Law of motion to conservation of momentum in collisions and explosions. c) Identify situations in which linear momentum, or a component of the linear momentum vector, is conserved. d) Apply linear momentum conservation to determine the final or initial velocities of two bodies when they collide, rebound, or stick together in one or two dimensions. Reading assignments - Chapter 9 - I highly recommend you read the Supplemental Reading Chapter 7 from Paul Hewitt s Conceptual Physics. 2

3 Impulse - Momentum Assignments # Assignment Due Date 1 Read Section Examples Textbook Section 7.1 # s: 1, 5, 9 Workbook Problem #: 1, 2 2 Read Section Examples Textbook Section 7.2 # s: 15, 47 Workbook Problem #: 3, 4 3 Read Section Examples Textbook Section 7.3 # s: 25 Workbook Problem #: 5, 6 4 Read Section Examples Textbook Section 7.3 # s: 28 (v f = 4.9 m/s), Workbook Problem #: Quiz Friday 1/29/03 Unit Test Friday - 2/5/03 Study suggestions Highly recommend that in small groups, discuss the Reviewing Concepts and Applying Concepts sections on page Look at the Chapter Objectives and make sure you are able to do all the objectives. Come seek help during lunch, or after 6 th Period every day to see me, get help with adult tutors in the Tutorial Center, OR see me about matching up with my AP Physics Student TUTORS. 3

4 1. A baseball (m = 0.14 kg) has an initial velocity of V o = -38 m/s as it approaches a bat. The bat applies a force that is much larger than the weight of the ball, and the ball departs from the bat with a final velocity of V f = 58 m/s. A. Calculate the impulse applied to the ball by the bat. B. Assuming that the time of contact, t = 1.6 x 10-3 s, predict the average force exerted on the ball by the bat. C. Sketch a qualitative graph of Force vs. Time. Show both the actual impulse and the approximation made by the average force vs. time. 4

5 2. During a storm, rain comes straight down with an initial speed of V o = 15 m/s and hits a car perpendicular to the surface of the roof. The mass of rain per second that strikes the car s roof is kg/s. A. Assuming that the rain comes to rest upon striking the car, predict the average force exerted by the roof on a rain drop. B. Suppose hailstones are falling on the roof with the same initial conditions as the rain drops. However, unlike rain drops, hailstones bounce off the roof of the car with the same final speed as its initial speed. Predict the average force exerted by the roof on a hail stone. 5

6 3. A freight train is being assembled in a switching yard. Car 1 has a mass of m 1 = 65 x 10 3 kg and moves at an initial speed of V 10 = 1.20 m/s. Car 2 has a mass of m 2 = 92 x 10 3 kg and an initial speed of V 2o = 0.80 m/s. Car two is behind and moving towards car 1. A. Predict the final velocity of the two cars after they collide & couple together in a perfect inelastic collision. V 1o V 2o C o ll Car 1 Car 2 i s Car 1 Car 2 i o n 6

7 4. Starting from rest, two ice skaters push off against each other on smooth level ice, where friction is negligible. The skater on the left has a mass of 54.0 kg and the other 88.0 kg. After the push, the skater on the left moves away with a speed of V 1f = 2.5 m/s. A. Predict the final velocity of the second skater. 7

8 5. An astronaut is motionless in outer space. Upon command, the propulsion unit strapped to his back ejects some gas with a velocity of 32 m/s, and the astronaut recoils with a velocity of -0.3 m/s. After the gas is ejected the mass of the astronaut is 160 kg. A. Predict the mass of the ejected gas. 8

9 6. Tragedy has overcome Circus City. One of the performers was injured in an accident. Peter, a kg circus performer, needs a new partner to perform the famous colliding loop-the-loop trick. The trick requires Peter to speed towards his partner, who is standing at rest at the bottom of a vertical loop, in-elastically collide (stick together) and safely slide around a vertical loop (4.50 m radius). The circus decides to use a 50.0 kg leopard as Pete s new partner. Assuming there is no friction anywhere along the path A. Predict the minimum speed necessary, at the bottom of the loop, such that Peter and the leopard can safely complete the trick. B. Predict Peter s initial speed before colliding with the leopard such that after the collision they can safely complete the trick. 9

10 7. Consider Tarzantha (M T = 64.2 kg) initially sitting at rest at the end of a long vine, L = 16.4 m, as shown in the diagram. On the ground below is a stranded explorer (M E = 56.6 kg) about to be attacked by a hungry tiger. Tarzantha pendulum swings down toward the explorer, grabs them in an inelastic collision, and swings upward toward safety. A. Predict Tarzantha s speed just before she collides with the explorer. B. Predict their speed just after the inelastic collision. The tiger can jump a maximum distance upward of 4.50 m. C. Predict the maximum height they could swing to. If Tarzantha and the explorer can stop at the maximum height, are they safe? L 10