# Chapter 9: Momentum, Work, Power Flashcards

What does area under a graph of force-time give?

Impulse (change in momentum)

*Momentum equation

momentum = mass x velocity

units: kgms^{-1}

What would happen when a ball(1) of velocity v with mass m hits a stationary ball(2) of the same mass

Ball(1) would stop on impact, ball (2) would move off with the same velocity v, conserving momentum

What would happen when a ball(1) of velocity v with mass m hits a stationary ball(2) that is much heavier

Ball(1) would rebound off of it, while ball(2) would move only a bit slowly as a response

How is momentum conserved in collisions and explosions

The momentum before is the same as the momentum after.

mass before * velocity before = mass after * velocity after

Is momentum a vector or scalar

Vector, the equation for momentum contains velocity, which is a vector

use the equation ‘mv’ to show conservation of momentum between a ball of velocity v hitting a stationary ball, both have same mass

mv + 0 = mv

=> 0 + mv = mv

State Newton’s First Law - the Law of Inertia

A body at rest will stay at rest (and a body in constant motion will stay in constant motion) unless a resultant external force acts on it.

State Newton’s Second Law.

The acceleration of an object is directly proportional to the resultant force applied to it (F = ma).

How does Newton’s second law apply to momentum?

The rate of change of momentum is directly proportional to the force F = Δp / Δt = ma

Δp = mΔv

What is impulse of a force?

The force multiplied by the time the force is applied for, so impulse is equal to the change in momentum Δp = FΔt

How do you increase impulse?

Increase the force, or the time it acts for (or both)

How are crumple zones in cars used for improved driver safety

They reduce the force on the driver as momentum is constant, and Δp = FΔt crumple zones increase the duration of the crash, so change in time increases, but to keep change in momentum constant, the force decreases so the force on the passenger decreases, improving their safety

How do seat belts airbags improve safety?

They reduce the force on the driver as momentum is constant, and Δp = FΔt seat belts stretch slowly and air bags deflate gradually, increasing how long it takes for a person to come to a halt if the car comes to a halt

How do you find impulse from a force-time graph?

The area under a force time graph between 2 time points on the X-axis give the impulse

What does area under a graph of force-time give?

Impulse (change in momentum)

What does the peak of the force-time graph give?

Maximum deformation of an object

State Newton’s third law

If body A exerts a force on body B then body B exerts an equal and opposite force on body A

Equation of force for free falling object near earth’s surface?

F = m g

m is mass in kg

g is acceleration usually 9.81 ms^{-2}