Physics - 0625 CIE

Momentum

Overview

A loaded lorry rolling slowly can do far more damage than a fast tennis ball, and a rifle kicks backwards the instant a bullet leaves it. Both facts come from one powerful idea: momentum. It combines how much matter is moving with how fast it moves, and it obeys a conservation law that lets you predict what happens in collisions and explosions.

In this Supplement topic you will define momentum and impulse, link force to the rate of change of momentum, and use conservation of momentum to solve one-dimensional collision problems. You will also see why crumple zones and 'following through' in sport both come down to changing momentum over a longer or shorter time.

Objectives

[Supplement] Define momentum as mass × velocity; recall and use the equation p = mv
[Supplement] Define impulse as force × time for which force acts; recall and use the equation impulse = F∆t = ∆(mv)
[Supplement] Apply the principle of the conservation of momentum to solve simple problems in one dimension
[Supplement] Define resultant force as the change in momentum per unit time; recall and use the equation ∆p F = ∆t

Lesson Note

Momentum explains crashes, rockets, recoil and sport. Crumple zones, air bags and catching a ball gently all work by controlling how quickly momentum changes. In the exam, momentum is a reliable source of calculation marks: you are expected to use \( p = mv \), conservation of momentum, and the force equation confidently.

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Lesson Evaluation

Congratulations on completing the lesson on Momentum. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.

You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.

Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.

The momentum of a 4 kg object moving at 5 m/s is: A. 0.8 kg m/s B. 20 kg m/s C. 9 kg m/s D. 1.25 kg m/s Answer: B
Impulse is equal to: A. mass times acceleration B. force times distance C. the change in momentum D. mass times velocity squared Answer: C
A 2 kg trolley at 6 m/s hits a stationary 4 kg trolley and they move off together. Their common velocity is: A. 6 m/s B. 3 m/s C. 2 m/s D. 12 m/s Answer: C
Crumple zones reduce the force in a crash because they: A. increase the change in momentum B. increase the collision time C. reduce the mass of the car D. increase the speed of impact Answer: B
A resultant force equals: A. momentum times time B. change in momentum per unit time C. mass per unit velocity D. velocity per unit time Answer: B