Physics 130: Questions to study for midterm #1 from Chapter 6

Transcription

1 Physics 130: Questions to study for midterm #1 from Chapter 6 1. Which has the greater momentum, an 18-wheeler parked at the curb or a Volkswagen rolling down a hill? a. 18-wheeler b. Volkswagen c. The momenta are equal. d. Could be either. 2. Linear momentum is defined to be a. mass times speed. b. mass times velocity. c. mass times acceleration. d. weight times velocity. 3. If a sports car with a mass of 1000 kg travels down the road with a speed of 30 m/s, its momentum is 30,000 a. kg/(m/s) b. kg s/m c. kg m/s d. kg m 2 /s 2 4. If a sports car with a mass of 1000 kg travels down the road with a speed of 40 m/s, its momentum is a. 100 kg/m/s b. 20,000 kg m/s c. 40,000 kg m/s d. 400,000 kg m 2 /s 2 5. How fast would you have to throw a baseball (m = 145 g) to give it the same momentum as a 10-g bullet traveling at 800 m/s? a m/s b. 1.8 m/s c. 55 m/s d. 800 m/s 6. Newton's second law can be rearranged to show that the is equal to the. a. momentum... impulse b. change in momentum... change in impulse c. change in momentum... impulse d. momentum... change in impulse

2 7. Padded dashboards in automobiles are safer because the a. momentum change is less b. impulse is less c. impact time is less d. impact time is greater 8. The stunt person who is shot by a bandit and falls from the balcony into an air bag rather than onto the ground will not be hurt because the a. momentum change is less for the air bag. b. momentum is less for the air bag. c. impulse is less for the air bag. d. increased stopping time means a smaller stopping force. 9. Why is skiing into a wall of deep powder less hazardous to your health than skiing into a wall of bricks? Assume in both cases that you have the same initial speed and come to a complete stop. a. The change in momentum is less in powder. b. The impulse is less in powder. c. The increased stopping time in powder means a smaller stopping force. d. The decreased stopping time in powder means a larger stopping force. 10. An astronaut training at the Craters of the Moon in Idaho jumps off a platform in full spacewalk gear and hits the surface at 5 m/s. If later on the Moon the astronaut jumps from the LEM and hits the surface at the same speed, the impulse will be that on Earth. a. the same as b. larger than c. smaller than 11. Assuming that your author jumps off the roof of a garage and lands on the ground. How will the impulse the ground exerts on him if he lands on grass compare to that if he lands on concrete? a. The impulse will be larger if he lands on concrete. b. The impulse will be larger if he lands on grass. c. The impulses will be the same independent of the surface. 12. Which of the following will cause the largest change in the momentum of an object? A force of acting for. a. 3 N... 6 s b. 4 N... 5 s c. 5 N... 5 s d. 6 N... 3 s 13. What is the impulse of a 5 N force acting for 15 s? a. 3 N s b. 15 N s c. 20 N s d. 75 N s 2

3 14. What change in momentum occurs when a force of 20 N acts for 4 s? a. 5 kg m/s b. 16 kg m/s c. 24 kg m/s d. 80 kg m/s 15. What impulse is need to stop a 1200-kg car traveling at 20 m/s? a. 60 N s b. 240 N s c N s d. 24,000 N s 16. A 1400-kg car has a speed of 20 m/s. What average force is required to stop the car in 10 s? a. 70 N b. 700 N c N d. 280,000 N 17. It takes about 30 s for a jet plane to go from rest to the takeoff speed of 100 mph (44.7 m/s). What is the average horizontal force that the seat exerts on the back of a 80-kg passenger during takeoff? a N b N c. 119 N d. 11,300 N 18. A very hard rubber ball (m = 0.6 kg) is falling vertically at 6 m/s just before it bounces on the floor. The ball rebounds back at essentially the same speed. If the collision with the floor lasts 0.04 s, what is the average force exerted by the floor on the ball? a. 45 N b. 90 N c. 180 N d. 360 N 19. If rockets are fired from an airplane in the forward direction, the momentum of the airplane will a. decrease. b. be unchanged. c. increase. 20. We can explain the recoil that occurs when a rifle is fired by using a. conservation of momentum. b. equal and opposite impulses. c. equal and opposite changes in momentum d. Any of the above. 3

4 21. A single firecracker explodes and breaks up into many pieces in the absence of air resistance. Compared to the momentum of the intact firecracker before the explosion, the vector sum of the momentum of the firecracker pieces after the explosion is a. less. b. greater. c. the same. d. could be more or less depending on the nature of the explosion 22. Greg runs across the front of the classroom with a momentum of 300 kg m/s and jumps onto a giant skateboard. The skateboard is initially at rest and has a mass equal to Greg s. If we ignore friction with the floor, what is the total momentum of Greg and the skateboard? a. zero b. 150 kg m/s c. 300 kg m/s d. 600 kg m/s 23. Carmen is standing on a giant skateboard that is initially at rest. If we ignore frictional effects with the floor, what is the momentum of the skateboard if Carmon walks to the right with a momentum of 500 kg m/s? a. 500 kg m/s to the right b. 500 kg m/s to the left c. 500 kg m/s d. zero 24. Two air-track gliders are held together with a string. The mass of glider A is twice that of glider B. A spring is tightly compressed between the gliders. If the gliders are initially at rest and the spring is released by burning the string, what is the total momentum of both gliders after the release? a. twice the momentum of A b. half the momentum of A c. twice the momentum of B d. zero 25. A 2-kg ball traveling to the right with a speed of 3 m/s collides with a 4-kg ball traveling to the left with a speed of 2 m/s. The total momentum of the two balls after the collision is kg-m/s to the. a left b right c right d left 4

5 26. A father (m = 90 kg) and son (m = 45 kg) are standing facing each other on a frozen pond. The son pushes on the father and finds himself moving backward at 3 m/s after they have separated. How fast is the father moving? a. 1 m/s b. 1.5 m/s c. 3 m/s d. 6 m/s 27. A more massive SUV collides with a less massive Honda Civic on a flat icy road. Which car experiences a larger magnitude of impulse resulting from the collision? a. the SUV b. the Civic c. the answer depends on how the vehicles are constructed d. both experience the same magnitude of impulse 28. A more massive SUV collides with a less massive Honda Civic on a flat icy road. Which car experiences a larger magnitude of momentum change resulting from the collision? a. the SUV b. the Civic c. the answer depends on how the vehicles are constructed d. both experience the same magnitude of momentum change 29. A more massive SUV collides with a less massive Honda Civic on a flat icy road. The mass of the driver of the SUV is equal to the mass of the driver of the Civic. Which driver experiences a larger magnitude of stopping force resulting from the collision? a. the driver of the SUV b. the driver of the Civic c. the answer depends on the time durations of the stopping forces d. both experience the same magnitude of stopping force 30. The momentum of a 2 kg object traveling north at 3 m/s is the momentum of a 1 kg object traveling east at 6 m/s. a. the same as b. not the same as c. less than d. greater than 5