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Advanced Physics Recap – Momentum | Adrian (2026)

Momentum

Adrian (2026)

Tuesday, 25 August 2026

01

Collision and Sticking

Combined motion after a collision

A moving trolley collides with a stationary trolley, and they stick together. Why must their combined speed be lower than the first trolley’s original speed?

3 marks
02

Momentum Transfer

Equal and opposite changes

During a collision, one object gains momentum. What must happen to the momentum of the other object? Explain using direction.

3 marks
03

Direction of Momentum

A ball rebounding from a wall

A ball hits a wall and rebounds at the same speed. Has its momentum changed even though its speed is unchanged? Explain.

3 marks
04

Mass and Velocity

Objects with equal momentum

Two objects have equal momentum but very different masses. What can you conclude about their velocities?

3 marks
05

Vehicle Collision

Truck and car momentum changes

A heavy truck and a small car collide. The truck’s change in momentum is large. How does the car’s change in momentum compare?

3 marks
06

Recoil

Throwing a bag from a skateboard

A person standing on a stationary skateboard throws a heavy bag forward. Explain why the person moves backward.

3 marks
07

Opposing Motions

Identical trolleys colliding

Two identical trolleys move towards each other at equal speeds. After colliding, they stick together. Predict their final motion and justify your answer.

3 marks
08

Separation and Explosion

An object breaking into two pieces

A moving object suddenly breaks into two pieces. One piece moves faster in the original direction. What are the possible motions of the other piece?

3 marks
09

Energy Changes

Momentum and kinetic energy

Momentum is conserved in a collision, but kinetic energy may decrease. Where might the “lost” kinetic energy go?

3 marks
10

Conservation Conditions

Momentum of an object and a system

A student says, “Momentum is conserved for every individual object during a collision.” What is wrong with this statement, and when can momentum be considered conserved?

3 marks

Question 1

  • The total momentum before and after the collision is the same if external forces are negligible.
  • Before the collision, only the first trolley carries momentum.
  • After the collision, the same momentum is shared by the greater combined mass of both trolleys.
  • The greater moving mass must therefore have a lower speed.

Question 2

  • The other object must undergo an equal change in momentum in the opposite direction.
  • If one object’s momentum increases in one direction, the other object’s momentum changes by the same amount in the opposite direction.
  • The total momentum change of the two-object system is zero.

Question 3

  • Momentum is a vector quantity and depends on both speed and direction.
  • The ball has the same speed after rebounding, so the magnitude of its momentum is unchanged.
  • Its direction of motion is reversed.
  • Its momentum has changed because its momentum now points in the opposite direction.

Question 4

  • Momentum depends on both mass and velocity.
  • For equal momentum, a greater mass must be associated with a smaller velocity magnitude.
  • A smaller mass must be associated with a greater velocity magnitude.
  • Mass and velocity magnitude are inversely related when momentum is fixed.

Question 5

  • During the collision, the truck and car exert equal and opposite forces on each other for the same time.
  • Their momentum changes are therefore equal in magnitude and opposite in direction.
  • The car’s change in momentum is just as large as the truck’s change in momentum.
  • The car may experience a greater change in velocity because its mass is smaller.

Question 6

  • The person, skateboard and bag are initially stationary, so their total momentum is zero.
  • Throwing the bag gives it forward momentum.
  • The person and skateboard must gain equal momentum in the opposite direction.
  • The person moves backward so that the total momentum remains zero.

Question 7

  • The two trolleys have equal momentum magnitudes because their masses and speeds are equal.
  • Their momenta point in opposite directions.
  • Their total momentum before the collision is zero.
  • After sticking together, the combined trolleys remain stationary.

Question 8

  • The total momentum of both pieces must equal the original object’s momentum if external forces are negligible.
  • The other piece may continue in the original direction at a lower speed.
  • It may become stationary.
  • It may move in the opposite direction if the faster piece carries more forward momentum than the original object had.
  • Its motion depends on the masses and momentum of the two pieces.

Question 9

  • Some kinetic energy may be transferred into thermal energy.
  • Some may be transferred into sound energy.
  • Some may be stored as energy associated with deformation of the objects.
  • It may also produce vibration or internal motion.
  • The energy is transformed, not destroyed.

Question 10

  • An individual object’s momentum usually changes during a collision because it experiences a force from the other object.
  • Momentum conservation applies to the total momentum of the complete interacting system.
  • The system must include all objects involved in the interaction.
  • The net external force on the system must be zero or negligible during the interaction.
  • Total momentum is conserved in an isolated system, not necessarily for each individual object.
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