Force & Momentum Flashcards

All 7 cards in this deck

What is the equation linking force, change in momentum and time?

$F = \dfrac{m\,\Delta v}{\Delta t}$

What does the equation $F = \dfrac{m\,\Delta v}{\Delta t}$ mean in words?

Force equals the rate of change of momentum.

What are the steps to calculate the change in momentum of an object?

e.g. a 1200 kg car slows from 20 m/s to 5 m/s

1. Find the change in velocity: $\Delta v = 20 - 5 = 15$ m/s
2. Use $\Delta p = m\,\Delta v$
3. $\Delta p = 1200 \times 15 = 18\,000$ kg m/s

What are the steps to calculate the average force during a collision from the change in momentum?

e.g. change in momentum 700 kg m/s in 0.28 s

1. Use $F = \dfrac{m\,\Delta v}{\Delta t}$
2. Substitute: $F = 700 \div 0.28$
3. $F = 2500$ N

In $F = \dfrac{m\,\Delta v}{\Delta t}$, what quantity does $\dfrac{\Delta v}{\Delta t}$ represent?

Acceleration — so the equation is equivalent to $F = m\,a$.

True or false? For the same change in momentum, a longer collision time means a smaller average force.

True. Force is the rate of change of momentum, so a bigger $\Delta t$ gives a smaller $F$.

True or false? For the same change in velocity in the same time, a heavier object needs a bigger force.

True. Its change in momentum $m\,\Delta v$ is larger, so the rate of change of momentum is larger.