P2.3 Work, Energy And Momentum

Question 1

Name the 9 types of energy

Answer 1

Thermal
Light
Nuclear
Chemical
Elastic potential 
Gravitational potential
Kinetic
Electricity 
Sound

Question 2

What does it mean if an object has done work?

Answer 2

It has transferred energy

Question 3

What’s work done measured in?

Answer 3

Joules (J)

Question 4

How do you work out work done?

Answer 4

Force X distance

Question 5

How do you work out power?

Answer 5

Work done/time

Question 6

What’s power measured in?

Answer 6

Watts (W)

Question 7

What objects have gravitational potential energy

Answer 7

Any object that’s raised above the ground

Question 8

How’d you work out GPE?

Answer 8

Mass X gravitational field strength X height

Question 9

What’s gravitational potential energy measured in?

Answer 9

Joules (J)

Question 10

What’s gravitational field strength measured in?

Answer 10

N/kg

Question 11

What objects have kinetic energy?

Answer 11

Any object that moves

Question 12

How do you work out kinetic energy?

Answer 12

1/2 X mass X velocity squared

Question 13

What’s kinetic energy measured in?

Answer 13

Joules (J)

Question 14

What objects have momentum?

Answer 14

Any object that moves

Question 15

How do you work out momentum?

Answer 15

Mass X velocity

Question 16

What’s momentum measured in?

Answer 16

kgm/s

Question 17

What’s the conservation of momentum?

Answer 17

The total momentum before an event = the total momentum after an event

Question 18

A railway engine of mass 800kg travelling at 5m/s collides with and becomes attached to a truck of 200kg travelling at 2m/s. Calculate the speed of the truck and engine after the collision.

Answer 18

Before: (800x5)+(200x2) = 4400 kgm/s
After: 4400kgm/s 
           800+200 = 1000kg
V=P/m       4400/1000 = 4.4 m/s
                                           --------

Question 19

A 0.5 kg trolley is pushed at a velocity of 1.2 m/s into a stationary trolley of mass 1.5 kg. The two trolleys stick to each other after the impact. Calculate the momentum before the collision and the velocity of the two trolleys.

Answer 19

P=VxM
=1.2 X 0.5 = 0.6 kgm/s

V= p/m
= 0.6/ (0.5+1.5)
=0.6/2
=0.3 m/s

Question 20

How do you calculate force?

Answer 20

Change in momentum/time

Question 21

When a force is applied to an object, the objects _________ changes. This means _________ also changes.

Answer 21

Velocity

Momentum

Question 22

How do seat belts provide car safety?

Answer 22

Seat belts work by stopping you from flying forward and hitting the windscreen or seat in front. In a collision they stretch slightly, which prolongs the time it takes for you to stop. This therefore reduces the size of the force on the body.

Question 23

How do airbags create car safety?

Answer 23

Airbags inflate almost instantly in a collision. They provide a soft cushion for your face and chest, and spread the force of impact over a larger area. Some cars also have airbags in the side to protect against side-impact collisions.

Question 24

How do crumple zones make car safety?

Answer 24

They’re in the front rear of the car and are designed to crumple gradually during a collision. This increases the duration of the collision, which reduces the size of the force and also absorbs some of the energy of the impact.

Question 25

What do side/impact bars do to make a car safer?

Answer 25

The bars absorb some energy of the collision so the car doesn’t crush into you sideways and stops the energy being passed onto you.

Question 26

What do normal brakes do?

Answer 26

When the brakes are applied work is done to slow the car down
The brakes reduce the kinetic energy by transferring it to heat energy (it’s wasted)

Question 27

What do regenerative brakes do?

Answer 27

Uses the drive system to brake
The brakes put the motor into reverse (when the motor runs backwards the wheels are slowed)
The motor acts as an electric generator - converting kinetic energy into electrical energy
This is stored as chemical energy in the battery

Question 28

What’s better about regenerative braking compared to normal braking?

Answer 28

Regenerative braking transfer energy whereas normal breaking wastes it

Question 29

Why is an aerodynamic vehicle good?

Answer 29

Means less air resistance so higher speed before the forces balance
Quicker