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Question 1 An open cart rolls along on frictionless axles while it is raining. As it rolls, what happens to the speed of the cart as the rain collects.

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Presentation on theme: "Question 1 An open cart rolls along on frictionless axles while it is raining. As it rolls, what happens to the speed of the cart as the rain collects."— Presentation transcript:

1 Question 1 An open cart rolls along on frictionless axles while it is raining. As it rolls, what happens to the speed of the cart as the rain collects in it? (Assume that the rain falls vertically into the cart.) A)speeds up B)maintains constant speed C)slows down D)stops immediately

2 Question 2 An 18-wheeler and a Volkswagon Beetle are rolling along with the same momentum. If you exert the same force with the brakes to stop each one, which takes a longer time to bring to rest? A)18-wheeler B)Volkswagon beetle C)same for both D)impossible to say

3 Question 3 Which is an example of a perfectly elastic collision? A)A wet tissue thrown at the wall. B)The cue ball striking the 8-ball in a billiards game. C)A rubber ball bouncing off the floor.

4 Question 4 An astronaut is taking a space walk when his tether breaks. He has a big drill. How can he get back to the space ship? A)Face away from the ship and throw the drill forward B)Face the ship and throw the drill forward. C)Throw the drill towards the tether.

5 Question 5 Car A is traveling west with speed 20 m/s when it collides with Car B, traveling east at 10 m/s. Which of the following are possible velocities of the cars after the collision? The cars have the same mass. A) Car A 10 m/s west, Car B 20 m/s east B) Car A 5 east, Car B 25 m/s west C) Both cars 5 m/s west D) Car A 18 m/s west, Car B 2 m/s west

6 Question 6 The square shown below is clearly has its center of mass at the center. Suppose the square is cut in two pieces and the pieces are rearranged as shown. The center of mass of this object has moved A)up and to the right. B)up and to the left. C)up only. D)down and to the left. E)down and to the right.

7 Question 7 As a kid playing on the playground, you would bend your knees when you landed after jumping off the monkey bars to reduce the "sting" in your feet. This worked because A)bending your knees gave you upward momentum which partly canceled the downward momentum. B)bending your knees lowered your center of gravity reducing the force of your fall. C)bending your knees increased the time of contact for the ground to bring you to rest. D)you didn't do it on purpose, your knees just buckled.

8 Question 8 As a linebacker on the football team, which player would be the easiest for you to stop when you tackle him? A)The 350-lb lineman who can cover 10 yards in 2.5 seconds. B)The 160-lb running back, who can make it down the field in ten seconds. C)The 240-lb halfback, who can make it down the field in twenty seconds. D)They are all equally hard to stop.

9 Question 9 Two forces produce equal impulses, but the second force, F 2, acts for a time twice that of the first force, F 1. Which force, if either, is larger? A)F 1 B)they are the same C)F 2

10 Question 10 A 280-lb linebacker running down the field at 7 m/s tackles a 240-lb halfback running up the field at 9 m/s. Will the halfback gain or lose yards after he is tackled? A)gain B)lose C)neither gain nor lose

11 Question 11 Two objects with different masses have the same kinetic energy. Which has the larger magnitude of momentum? A)the larger mass B)the smaller mass C)they have the same momentum D)impossible to tell

12 Question 12 Maggie drops a stuffed bear over the side of her crib. It hits the floor with speed v and comes to rest. She then drops a rubber ball with the same mass from the same height, and it bounces back upwards with speed v. Compare the change in momentum of the bear and the ball. A)  p bear =  p ball B)  p bear = 2  p ball C)  p bear = ½  p ball D)  p bear = -  p ball

13 Question 13 You peddle frantically to get your bicycle up to a speed of 15 m/s. On level ground, you relax and start to coast. Your speed A)stays the same, because momentum is conserved. B) increases, now that you are not expending energy turning the pedals. C) decreases, as there are still forces acting on the bicycle.

14 Question 14 An urban legend has it that the RAF was testing the windshields of their aircraft for bird strikes using a chicken cannon given to them by the USAF. The windshields kept breaking because they were using frozen chickens instead of fresh ones. Using your knowledge of physics, you would reason that the legend is A)false - frozen and thawed chickens have the same momentum on impact. B)true - frozen chickens are harder and come to rest in a shorter time, increasing the force.

15 Question 15 You paddle your own canoe forward by pushing back on the water. If you can change the velocity of 7.3 kg of water by 3.0 m/s with each stroke, your speed changes by (m you + m canoe = 93 kg) A)226 m/s B)38 m/s C)4.2 m/s D)0.24 m/s

16 Question 16 You are knocking out sheetrock with a sledge hammer. Which is more efficient, for you to swing the hammer so it stops at the surface of the sheetrock, or to swing the hammer so that it goes past the surface of the sheetrock before stopping? A)At the sheetrock, because the most energy is dissipated there. B)Past the sheetrock, so the hammer is in contact with the sheetrock for a longer time.

17 Question 17 A boxcar with mass m moving to the right with speed v collides with a second boxcar of the same mass which is at rest. After the collision, both boxcars move off to the right with speed v/2. In this collision A)momentum is conserved. B)energy is conserved. C)momentum and energy are conserved. D)neither momentum nor energy is conserved.

18 Question 18 Red Rover, Red Rover, let Leslie come over. In this childhood game, you try to stop and catch a person who is running directly at you. Who would you rather pick? A)Sean, who weighs 450 N and can run 5.4 m/s. B)Meihong, who weighs 270 N and can run 8.8 m/s. C)Deidra, who weighs 340 N and can run 7.2 m/s.

19 Question 19 Suppose you throw a rubber ball at an approaching truck. When it bounces back to you, is it traveling faster, slower, or with the same speed at which you threw it? A)faster B)slower C)at the same speed

20 Question 20 When you lift a heavy suitcase in one hand, you lean A)toward the suitcase, to move your center of gravity under the suitcase. B)away from the suitcase, to shift your center of gravity towards your feet. C)towards the suitcase, since it is weighing you down.

21 Answer Key – Chapter 7 1. C 2. C 3. B 4. A 5. C 6. B 7. C 8. C 9. A 10. A 11. A 12. C 13. C 14. B 15. B 16. B 17. A 18. A 19. A 20. B

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