Momentum and Changes in Momentum Flashcards

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What is momentum, and how do you calculate it?

Momentum is mass times velocity. p = m × v.

What are the SI units of momentum?

Kilogram metre per second (kg m/s).

Is momentum a scalar or a vector, and what does that mean?

It is a vector. It has size and direction, the same as the velocity.

How do you work out the change in momentum of an object?

Change in momentum = mass × (final velocity − initial velocity).

What equation links force, time, and change in momentum?

Force = change in momentum ÷ time taken.

Why do airbags, seat belts, and crumple zones help in a crash?

They increase the time to stop, so for the same change in momentum the average force is smaller.

What does conservation of momentum say about a collision or explosion in a closed system?

Total momentum before equals total momentum after if no external forces act.

For the same speed, why does a bouncing ball feel a bigger force than a ball that just stops?

Its velocity reverses, so the change in momentum is larger, which gives a larger force for the same time.

A 2.0 kg trolley moves at 3.0 m/s and hits a 1.0 kg trolley at rest. They stick together. What is their speed after?

Total momentum = 2.0 × 3.0 = 6.0 kg m/s. Total mass = 3.0 kg. Speed after = 6.0 ÷ 3.0 = 2.0 m/s (same direction).

A 1.5 kg ball is stopped from 8.0 m/s to 0 m/s in 0.40 s. What is the average force on it?

Change in momentum = 1.5 × (0 − 8.0) = −12 kg m/s. Force = −12 ÷ 0.40 = −30 N, so 30 N opposite to the motion.