# P2.4 Momentum, energy, work and power Flashcards

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1
Q

What is thinking distance?

A

The time taken for a driver to react

2
Q

What is the breaking distance?

A

The time taken for the brakes to make a car stop

3
Q

How do you find the stopping distance?

A

Stopping distance = thinking distance + breaking distance

4
Q

What happens to thinking distance when reaction time increases?

A

It increases

5
Q

What can affect reaction times?

A
• being tired
• being ill
• taking drugs or alcohol
6
Q

What does friction do to vehicles?

A

Slow them down

7
Q

How do brakes stop cars?

A

They cause a lot of friction

8
Q

What can affect the amount of friction created on a road?

A

The road being wet or having loose gravel

9
Q

As the mass of a vehicle increases, what happens to the force needed to decelerate it?

A

It increases

10
Q

What is momentum?

A

A measure of how strongly something is moving

11
Q

What is the equation for calculating momentum?

A

Momentum(kg m/s) = mass(kg) x velocity (m/s)

12
Q

What is a conservation of linear momentum?

A

When the total momentum of both objects is the same after the collision as before the collision

13
Q

How do seat belts protect people during a car accident?

A

They stretch to reduce the change of momentum and it therefore reduces the force acting on the passenger

14
Q

What are some benefits of air bags over seat belts?

A

They reduce momentum to zero more slowly and so prevent seat belt injuries

15
Q

How do crumple zones help during car accidents?

A

These crumple in a specific way to reduce the momentum of the car over a longer period of time

16
Q

How do you calculate force?

A
```Force (N) = change in momentum (kg m/s) /
time taken (s)```

F= mv-mu / t

17
Q

How do you calculate change in momentum?

A

Final velocity - initial velocity

mv-mu

18
Q

What is work?

A

The amount of energy transferred

19
Q

What is work measured in?

A

Joules (J)

20
Q

How do you calculate the amount of work done?

A
```Work = force  x distance moved
E = F x d```
21
Q

What is the equation for calculating power?

A
```Power = work done / time taken
P = E / t```
22
Q

How do you calculate the work done of stopping a car?

A

Breaking force x breaking distance

23
Q

What is gravitational potential energy?

A

The energy that is stored because of an object’s position in a gravitational field

24
Q

How do you calculate gravitational potential energy?

A

GPE(J) = mass(kg) x gravitational field strength(N/kg) x vertical height(m)

GPE = m x g x h

25
Q

What is the equation for calculating kinetic energy?

A

KE (J) = 1/2 x mass(kg) x velocity^2

KE = 1/2 x m x v^2