Differentiated Physics Practice Questions

Transcription

1 Differentiated Physics Practice Questions Multiple Choice Identify the choice that best completes the statement or answers the question. 1. A 100-kg cannon at rest contains a 10-kg cannon ball. When fired, the cannon ball leaves the cannon with a speed of 90 m/s. What is the recoil speed of the cannon? a. zero b. 9 m/s c. 4.5 m/s d. 90 m/s e. 45 m/s 2. A 0.1-kg steel ball is dropped straight down onto a hard horizontal floor and bounces straight up. Its speed just before and just after impact with the floor is 10 m/s. Determine the magnitude of the impulse delivered to the floor by the steel ball. a. 1 N s b. 10 N s c. zero N s d. 2 N s e. 100 N s 3. An 80-kg astronaut carrying a 20-kg tool kit is initially drifting toward a stationary space shuttle at a speed of 2 m/s. If she throws the tool kit toward the shuttle with a speed of 6 m/s as seen from the shuttle, her final speed is a. 1 m/s away from the shuttle. b. 1 m/s toward the shuttle. c. 2 m/s toward the shuttle. d. 6 m/s away from the shuttle. e. 4 m/s toward the shuttle. 4. A 3.0-kg cart moving to the right with a speed of 1.0 m/s has a head-on collision with a 5.0-kg cart that is initially moving to the left with a speed of 2 m/s. After the collision, the 3.0-kg cart is moving to the left with a speed of 1 m/s. What is the final velocity of the 5.0-kg cart? a. 0.8 m/s to the right b. 2.0 m/s to the right c. 2.0 m/s to the left d. 0.8 m/s to the left e. zero m/s 5. Complete the following statement: Momentum will be conserved in a two-body collision only if a. both bodies come to rest. b. the collision is perfectly elastic. c. the internal forces of the two body system cancel in action-reaction pairs. d. the net external force acting on the two-body system is zero. e. the kinetic energy of the system is conserved. 1

2 6. A baseball of mass m is struck by a bat so that it acquires a speed v. If t represents the duration of the collision between the bat and the ball, which expression determines the magnitude of the average force exerted on the ball? a. (1 / 2)mv 2 t b. mt 2 / (2v) c. (1 / 2)mv 2 d. mv / t e. mvt 7. A 1.0-kg ball has a velocity of 12 m/s downward just before it strikes the ground and bounces up with a velocity of 12 m/s upward. What is the change in momentum of the ball? a. zero kg m/s b. 24 kg m/s, upward c. 12 kg m/s, downward d. 12 kg m/s, upward e. 24 kg m/s, downward 8. A 50.0-kg boy runs at a speed of 10.0 m/s and jumps onto a cart as shown in the figure. The cart is initially at rest. If the speed of the cart with the boy on it is 2.50 m/s, what is the mass of the cart? a. 300 kg b. 210 kg c. 175 kg d. 260 kg e. 150 kg A comet fragment of mass kg is moving at m/s when it crashes into Callisto, a moon of Jupiter. The mass of Callisto is kg. The collision is completely inelastic. 9. Assuming for this calculation that Callisto's initial momentum is zero, what is the recoil speed of Callisto immediately after the collision? a m/s b m/s c m/s d m/s e m/s 2

3 10. A bat strikes a kg baseball so that its velocity changes by +30 m/s in 0.10 s. With what average force was the ball struck? a N b N c. +15 N d. -15 N e N 11. A 7.30-kg bowling ball strikes a 1.60-kg pin at rest head-on. Before the collision, the velocity of the ball is m/s. After the collision, the velocity of the ball is m/s. What is the velocity of the pin after the collision? a m/s b. +52 m/s c m/s d m/s e m/s 12. In which one of the following situations is linear momentum not conserved? a. An astronaut floating in space throws a hammer away and subsequently moves in the opposite direction. b. A bomb suspended by a string explodes into one hundred fragments. c. A bowling ball collides with ten pins. d. A tree limb is struck by lightning and falls to the ground. e. A golf ball is struck by a club. 13. A tennis ball has a velocity of 12 m/s downward just before it strikes the ground and bounces up with a velocity of 12 m/s upward. Which statement is true concerning this situation? a. The momentum of the ball is changed; the momentum of the earth is not changed. b. The momentum of the ball is unchanged; the momentum of the earth is changed. c. Neither the momentum of the ball nor the momentum of the earth changes. d. Both the momentum and the kinetic energy of the ball change because of the collision. e. The momentum of the ball and the momentum of the earth both change. 14. Two objects of equal mass traveling toward each other with equal speeds undergo a head on collision. Which one of the following statements concerning their velocities after the collision is necessarily true? a. Their velocities will be reduced. b. Their velocities will be unchanged. c. Their velocities will be zero. d. Their velocities may be zero. e. They will exchange velocities. 15. A 1000-kg car traveling east at 20 m/s collides with a 1500-kg car traveling west at 10 m/s. The cars stick together after the collision. What is their common velocity after the collision? a. 2 m/s, east b. 4 m/s, east c. 1 m/s, west d. 16 m/s, east e. 6 m/s, west 3

4 16. A football player kicks a 0.41-kg football initially at rest; and the ball flies through the air. If the kicker's foot was in contact with the ball for s and the ball's initial speed after the collision is 21 m/s, what was the magnitude of the average force on the football? a. 210 N b. 46 N c. 170 N d. 81 N e. 9.7 N 17. A machine gun fires 50-g bullets at the rate of 4 bullets per second. The bullets leave the gun at a speed of 1000 m/s. What is the average recoil force experienced by the machine gun? a. 200 N b N c. 10 N d. 100 N e. 20 N 18. A 58.5-kg astronaut is floating toward the front of her stationary ship at 0.15 m/s, relative to the ship. She wishes to stop moving, relative to the ship. She decides to throw away the 2.50-kg book she's carrying. What should the speed and direction of the book be to achieve her goal? a. 3.7 m/s, toward the front of the ship b m/s, toward the front of the ship c m/s, toward the back of the ship d. 1.8 m/s, toward the front of the ship e. 3.5 m/s, toward the back of the ship 19. A 35-kg girl is standing near and to the left of a 43-kg boy on the frictionless surface of a frozen pond. The boy tosses a 0.75-kg ice ball to the girl with a horizontal speed of 6.2 m/s. What are the velocities of the boy and the girl immediately after the girl catches the ice ball? girl boy a m/s, left 0.14 m/s, left b m/s, right 0.13 m/s, left c m/s, left 0.67 m/s, right d m/s, left 0.11 m/s, right e m/s, left 0.49 m/s, right 4

5 A 2.0-kg pistol fires a 1.0-g bullet with a muzzle speed of 1000 m/s. The bullet then strikes a 10-kg wooden block resting on a horizontal frictionless surface. The block and the embedded bullet then slide across the surface. 20. The explosive charge in the pistol acts for s. What is the average force exerted on the bullet while it is being fired? a N b. 1.0 N c N d. 100 N e. 500 N 21. What is the speed of the "bullet + block" system immediately after the bullet is embedded in the block? a. zero b m/s c. 0.1 m/s d m/s e. 10 m/s 22. A kg lump of clay moving horizontally at 12 m/s strikes and sticks to a stationary 0.10-kg cart that can move on a frictionless air track. Determine the speed of the cart and clay after the collision. a. 6 m/s b. 8 m/s c. 4 m/s d. 12 m/s e. 2 m/s 23. Jennifer is walking at 1.63 m/s. If Jennifer weighs 583 N, what is the magnitude of her momentum? a. 137 kg m/s b. 672 kg m/s c kg m/s d kg m/s e. 951 kg m/s 5

6 A 4.0-kg block slides along a frictionless surface with a constant speed of 5.0 m/s. Two seconds after it begins sliding, a horizontal, time-dependent force is applied to the mass. The force is removed eight seconds later. The graph shows how the force on the block varies with time. 24. What, approximately, is the speed of the block at t = 11 seconds? a. 25 m/s b. 16 m/s c. 65 m/s d. 5.0 m/s e. 75 m/s 25. What is the magnitude of the total impulse of the force acting on the block? a. 48 N s b. 20 N s c. 60 N s d. 54 N s e. 42 N s 26. A kg tennis ball moving to the right with a speed of 15 m/s is struck by a tennis racket, causing it to move to the left with a speed of 15 m/s. If the ball remains in contact with the racquet for s, what is the magnitude of the average force experienced by the ball? a N b. 160 N c. zero newtons d N e. 98 N 27. Which one of the following is true concerning momentum? a. The SI unit of momentum is kg m 2 / s. b. Momentum is a scalar quantity. c. Momentum is a force. d. The momentum of an object is always positive. e. Momentum and impulse are measured in the same units. 6

7 28. A stunt person jumps from the roof of a tall building, but no injury occurs because the person lands on a large, air-filled bag. Which one of the following best describes why no injury occurs? a. The bag reduces the impulse to the person. b. The bag provides the necessary force to stop the person. c. The bag increases the amount of time during which the momentum is changing and reduces the average force on the person. d. The bag increases the amount of time the force acts on the person and reduces the change in momentum. e. The bag decreases the amount of time during which the momentum is changing and reduces theaverage force on the person. 29. Two cars of equal mass collide on a horizontal frictionless surface. Before the collision, car A is at rest while car B has a constant velocity of 12 m/s. After the collision, the two bodies are stuck together. What is the speed of the composite body (A + B ) after the collision? a. 30 m/s b. 6 m/s c. 12 m/s d. 3 m/s e. 24 m/s 30. The head of a hammer (m = 1.5 kg) moving at 4.5 m/s strikes a nail and bounces back with the same speed after an elastic collision lasting s. What is the magnitude of the average force the hammer exerts on the nail? a. 6.8 N b. 180 N c. 60 N d. 240 N e. 90 N 7