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Unit 7: Momentum and Collisions

The quantity that never disappears in a crash: how mass and velocity combine, and what a slow-motion replay shows before and after.

6 topics · 20 questions

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Momentum

  1. How it worksHow does momentum combine mass and velocity into a single quantity that points somewhere?
  2. Worked exampleFind the momentum of a 1000 kg car moving at 20 m/s.
  3. Common mistakeWhy isn't momentum the same thing as kinetic energy?
Your turn1 of 2
Find the momentum of a 2241 kg car moving at 26 m/s.

Impulse and Change in Momentum

  1. How it worksHow does a force applied over a longer time produce a smaller peak force for the same total impulse?
  2. Worked exampleFind the average force on a 0.15 kg baseball that changes momentum by 6 kg m/s in 0.01 seconds.
  3. Going furtherWhat happens to the force felt in a collision when the same impulse is stretched over ten times as long?
Your turn1 of 2
Find the average force on a 3.51 kg baseball that changes momentum by 19.65 kg m/s in 0.466 seconds.

Conservation of Momentum

  1. How it worksHow does the total momentum of a system stay exactly the same before and after a collision with no outside force?
  2. Worked exampleFind the final velocity of a 60 kg skater at rest after pushing off a 40 kg skater who moves away at 3 m/s.
  3. Common mistakeWhy doesn't momentum need to be conserved separately for each object in a collision?
  4. Going furtherWhat happens to the total momentum of a system when an outside force like friction is added?
Your turn1 of 2
Find the speed of a 79 kg skater at rest after pushing off a 75 kg skater who moves away at 7.47 m/s.

Elastic Collisions

  1. How it worksHow does an elastic collision conserve both momentum and kinetic energy at the same time?
  2. Worked exampleFind the final velocities of two equal-mass carts when a 2 m/s cart elastically hits an identical cart at rest.
  3. Common mistakeWhy isn't kinetic energy conserved in most everyday collisions?
Your turn1 of 2
A cart moving at 14.02 m/s elastically hits an identical, equal-mass cart at rest. Since equal masses exchange velocities in a head-on elastic collision, find the final velocity of the cart that was originally at rest.

Inelastic Collisions

  1. How it worksHow does a perfectly inelastic collision stick two objects together while still conserving total momentum?
  2. Worked exampleFind the common velocity after a 1200 kg car moving at 15 m/s collides and sticks with a stationary 1200 kg car.
  3. Common mistakeWhy doesn't a car that crumples in a crash violate the conservation of momentum?
  4. Going furtherWhat happens to a firework's fragments the instant it explodes from rest into pieces flying outward?
Your turn1 of 2
Find the common velocity after a 1893 kg car moving at 20 m/s collides and sticks with a stationary 2364 kg car.

Momentum in Two Dimensions

  1. How it worksHow does momentum have to be conserved separately along both the x and y directions in a glancing collision?
  2. Worked exampleFind the total momentum of a system where a 2 kg object moves at 3 m/s east and a 1 kg object moves at 4 m/s north.
  3. Going furtherWhat happens to the direction of the total momentum vector when two objects collide at a right angle to each other?
Your turn1 of 2
Find the magnitude of the total momentum of a system where a 14.08 kg object moves at 9.91 m/s east and a 18.68 kg object moves at 4.54 m/s north.