Edexcel A-Level Physics Impulse and Momentum Change

Practise Edexcel A-Level Physics impulse and momentum change by using collision time, rebound direction and vector changes in momentum.

Exam points

calculate impulse or mean force from collision time and vector change in momentum
identify the correct force magnitude and direction when an object rebounds from a wall or ground

[Maximum number: 2]

Some asteroids pass very close to the Earth. Scientists are planning methods to deflect asteroids, to prevent them hitting the Earth.

One method would involve colliding a spacecraft into the surface of the asteroid, to change the path and speed of the asteroid. The spacecraft would remain joined to the asteroid after the collision.

Another method would involve attaching a rocket motor to the asteroid and using the motor to apply a force to the asteroid.

In this method the force is applied at $90^\circ$ to the path of the asteroid. Deduce whether this would produce a change in momentum as great as the change produced by the collision method.

Force exerted by rocket motor = $5.1\times10^6\,\mathrm{N}$

Time for which rocket motor applies force = $6\,\mathrm{minutes}$

Use impulse $\Delta p=F\Delta t$ .

$\Delta p=(5.1\times10^6\,\mathrm{N})(6\times60\,\mathrm{s})=1.8\times10^9\,\mathrm{N\,s}$

This is greater than the $1.1\times10^7\,\mathrm{N\,s}$ change from the collision method.

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4.3.81 - Impulse and change of momentum question 1