Flashcards in Topic 4 - Momentum, Energy, Work and Power Deck (31):

1

## What is stopping distance?

### The distance it takes to stop a car, made up from thinking distance + braking distance

2

## What is thinking distance?

### The distance the car travels in the time between the driver noticing the hazard + applying the brakes

3

## What factors affect thinking distance?

###
-Reaction time: affected by tiredness, drugs, alcohol, age

-Fast you're going: faster you go, further thinking distance

4

## What is braking distance?

### The distance the car travels during its deceleration whilst the brakes are being applied, time between the brakes applied + car stopping

5

## What factors affect braking distance?

###
-Speed: faster = further braking distance

-Mass of vehicle: w/ same brakes, heavy = longer to stop

-Quality of brakes

-Grip: friction between tyres + road surface to stop (depends on road surface, weather, tyres)

6

## What experiment could you do to investigate how much frictional force different surfaces provide?

###
-Add masses 1 by 1 to mass holder to provide a force on block until eventually slides

-Amount of force (amount of mass) needed to slide block depends on amount of friction between block + surface (like tyres on road surfaces)

-Can use different surfaces

-Smaller frictional force between block + surface = smaller force to make block slide

7

## How does a greater mass/greater velocity affect momentum?

### More momentum of an object

8

## What is a vector?

###
-Has size

-Has direction

9

## Is momentum a vector?

### Yes

10

## What is the equation for momentum?

### Momentum = mass x velocity

11

## What is momentum measured in?

### kg m/s

12

## What is the relationship between momentum before and momentum when no external forces act?

###
-Equal

-Momentum is conserved

13

## What is the equation relating force, chance in momentum and time?

###
Force = change in momentum / time

mv-mu

F= t

14

## What is force measured in?

### Newtons

15

## Why are protective features put into cars?

###
-Slow people over a longer time when they crash

-Take a longer time to change momentum, decreasing force

16

## What protective features are out into cars to increase stopping distance and how does this make the car safer?

###
-Crumple zones: crumple on impact, increase time taken for car to stop

-Seat belt: stretch so increase time taken for wearer to stop reducing force on chest

-Air bags: slow you down more gradually

17

## How can bubble wrap and an egg be used to demonstrate how crumple zones work?

###
-Dropping egg on hard floor means they shatter

-Drop onto cushions in foam or build crumple zone of cardboard + bubble wrap

-Collisions happen over longer time so force on egg is smaller

-Reduces the force on the egg

18

## What causes work to be done?

### When a force moves an object, energy is transferred and work is done.

19

## What is work done measured in?

### Joules, J

20

## What is the formula for work done?

### Work done = force x distance moved in the direction of the force

21

## What is the formula linking power, work done and time taken?

### Power = work done / time taken

22

## What units can be used to measure power?

### Watts, W or J/s (joules of energy per second, 1 W = 1 joule of energy per second)

23

## What is the equation for kinetic energy?

### Kinetic energy = 0.5 x mass x velocity^2

24

## Initial kinetic energy = work done by brakes to stop vehicle. What is this in symbols and what happens to work done if you double your speed?

###
- 0.5 x m x v^2 (velocity) = F (maximum braking force) x d (braking distance)

-Double speed = 2xv, and as v^2 KE increases by factor 4

-F is always maximum possible braking force so d must be increased by factor 4 to balance

-So double speed = 4 x braking distance

25

## What is all energy measured in?

### Joules

26

## What is the equation for gravitational potential energy?

### GPE = mass x g (gravitational field strength, 10 N/kg) x height

27

## What is the gravitational field strength on earth?

### 10 N/kg

28

## What is the principle of conservation of energy?

### Energy can never be created nor destroyed, only transferred from one form to another

29

## What is a principle of energy being useful?

### Energy is only useful when it's transferred from one form to another.

30

## How does energy transfer in a falling object?

###
-GPE converted to KE (principle of conservation of energy)

-Some GPE likely dissipated as heat from air resistance

-Kinetic energy gained = Gravitation potential energy lost

31