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Momentum and collisionsPhysicsHigh schoolabout 0:46

An impulse of 12 N·s is delivered by an average force of 400 N. How long does the force act?: animated lesson

A narrated, step-by-step momentum and collisions video lesson with captions. Final answer: time interval Δt = 0.03 s.

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Video with a synthetic English voice and captions. Pick another language for subtitles in that language, or open the interactive version.

Video narrated by a synthetic voice (Piper TTS, en_US-ljspeech-high voice (LJ Speech dataset, public domain)); the steps come from our maths engine and the answer was checked independently. Download MP4 (0.3 MB) · Captions (WebVTT)

Steps on screen

1. The problem
Worked example
An impulse of 12 N·s is delivered by an average force of 400 N. How long does the force act?
2. Step by step
1. $J = F\,\Delta t = \Delta p$
  Formula: impulse
2. $\Delta t = \frac{J}{F}$
  Rearrange for time interval Δt
3. $\Delta t = \frac{(12)}{(400)} = 0.03\ \text{s}$
  Substitute the known values
3. The answer
$\text{time interval Δt = 0.03 s}$
time interval Δt = 0.03 s
4. Check
- Substituted every value back into the formula: both sides agree ✓

Transcript

The problem. Here is the problem: An impulse of 12 N times s is delivered by an average force of 400 N. How long does the force act? Use the impulse formula, rearranged for the unknown, in SI units.

Step by step. Formula: impulse. Rearrange for time interval deltat. Substitute the known values.

The answer. So the answer is time interval deltat equals 0.03 s. Impulse equals the change in momentum (impulse–momentum theorem). Spreading the same change in momentum over a longer time, as airbags and crumple zones do, reduces the average force.

Check. Substituted every value back into the formula: both sides agree, which checks out.

About momentum and collisions

Momentum, impulse and conservation of momentum in collisions.

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