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All 11 Flashcards — Momentum & impulse
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Question
Define momentum.
Answer
The **mass × velocity** of an object — how much motion it has. p = mv, unit kg m s⁻¹. It is a **vector** (has direction).
Question
Define impulse.
Answer
The **average force × the time** it acts for, J = FΔt. It equals the **change in momentum** (Δp). Unit: N s.
Question
What is the unit of momentum?
Answer
**kg m s⁻¹**. Impulse uses **N s**, which is the same unit.
Question
Formula for momentum?
Answer
$p = mv$ — mass × velocity (given in the data booklet).
Question
Formula for impulse?
Answer
$J = F\Delta t = \Delta p$ — force × time = change in momentum (given).
Question
How do you find the average force in a collision?
Answer
$F = \dfrac{\Delta p}{\Delta t}$ — the change in momentum ÷ the contact time (given form of Newton's 2nd law).
Question
What does the area under a force–time graph give?
Answer
The **impulse** — which equals the **change in momentum**.
Question
A ball bounces straight back at the same speed. Is its change in momentum zero?
Answer
**No** — the direction flips, so Δp = m(v + u) = 2mu. Bouncing changes momentum more than stopping.
Question
Why do air bags and crumple zones reduce injury?
Answer
They **increase the contact time** Δt. Since F = Δp/Δt, a longer time means a **smaller force** for the same change in momentum.
Question
A 0.50 kg ball at rest gets a 6.0 N s impulse. Final speed?
Answer
Δp = J = 6.0 kg m s⁻¹, so v = p/m = 6.0 ÷ 0.50 = 12 m s⁻¹.
Question
Link impulse to kinetic energy from rest.
Answer
Impulse gives momentum p = J; then $E_k = \dfrac{p^2}{2m} = \dfrac{1}{2}mv^2$ once you have the speed.
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Topic 1.2 hub
Forces and momentum
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