Momentum and Collisions Review

Two friends wearing frictionless roller skates are facing each other within arm's reach.  Jimi pushes gently on his friend Tony's upraised palms.  What happens?

• Both Jimi and Tony remain motionless.
• Jimi remains motionless, and Tony rolls away from him.
• Both Jimi and Tony remain motionless, unless they push on each other with enough force.  
• Jimi and Tony roll in opposite directions.

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May (61 kg) and Amber (56 kg) stand motionless on ice skates, facing each other at arm's length on a smooth, frozen pond.  Which of the following actions will give Amber the least speed?

• Amber pushes May with 300 N of force for 0.1 s.
• May pushes Amber with 80 N of force for 0.6 s.
• Amber pushes May with 400 N of force for 0.04 s.
• Amber pushes May with 500N of force for 0.08 s.

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A 3.0 kg ball of clay traveling at 10 m/s collides with a 20 kg ball of clay traveling in the same direction at 2.0 m/s.  What is their combined speed if the two balls stick together when they touch?

• 70 m/s
• 3.0 m/s
• 1.9 m/s
• 1.0 m/s

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A motionless 130 kg astronaut is holding a 9.9 kg tool while on a spacewalk.  To get moving, the astronaut throws the tool forward at a speed of 8.0 m/s.  How fast does the astronaut move backward?

• 0.062
• 0.61 m/s
• 0.076 m/s
• 2.8

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A 2800 kg truck moving at 19 m/s collides with a stationary 1000 kg passenger car, and the two stick together.  Assuming that they are free to move afterward, what is the momentum of the truck + car object after the collision?

• 14,000 kg*m/s
• 14 kg*m/s
• 72,000 kg*m/s
• 53,000 kg*m/s

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A model rocket with an initial mass of 4.0 kg is launched horizontally by burning and expelling 530 g of fuel with a velocity of 100 m/s.  What is the velocity of the rocket after the fuel is expelled?  (Assume the propellant is expelled instantaneously.)

• 15 m/s
• 0.65 m/s
• 13 m/s
• 66 m/s

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A steel ball traveling at 6 m/s hits a stationary line of three steel balls.  Which statement is true if the collision is perfectly elastic? 

• The original ball stops and the three balls move to the right at 2 m.s.
• The original ball stops and a single ball moves to the right at 6 m/s.
• The original ball bounces back at -3 m/s and one ball moves to the right at +3 m/s.
• All four balls move to the right at 1.5 m.s.

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A spacewalking astronaut is stranded a few meters from the space station door. His jet pack is broken, but he can take it off and toss it in order to propel himself toward the door.  In what direction should he toss it?

• The direction depends on the jet pack's mass.
• It should be tossed to the right of the door?
• It should be tossed toward the Earth.  
• It should be tossed away from the door.  

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Ball A has a mass of 8.0 kg.  Ball B has twice the mass of ball A.  The two balls collide and stick together in a perfectly inelastic  collision.  After the collision the combined balls are at rest.  If the velocity of ball A before the collision was 7.3 m/s , what was the velocity of ball B before the collision?

• 3.6 m/s
• -7.3 m/s
• 15 m/s
• -3.6 m/s

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In an inelastic collision, what quantities are conserved?

• momentum and kinetic energy
• kinetic energy only
• It depends on the masses of the colliding objects.
• momentum only 

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