Year 9 physics exam

Question 1

What are the 5 energy stores?

Answer 1

1. Chemical stores of energy

e.g. energy in fuel, foods, batteries

2. Kinetic stores of energy

e. g. energy in moving objects

2. Gravitational potential stores of energy

e. g. energy of an object because of its position to the ground

3. Elastic potential stores of energy

e. g. energy of a stretched or squashed object

4. Thermal stores of energy

e. g. energy of an object because of its temperature

Question 2

What is an energy store associated with a compressed spring?

Answer 2

Elastic potential energy

Question 3

What is the energy associated with a book on a high shelf?

Answer 3

gravitational potential energy

Question 4

How can energy be transferred?

Answer 4

Engergy can be transferred by:

1. Heating
2. Waves
3. Electrical current
4. Force when it moves an object

Question 5

Describe the energy transfer when an object falls to the ground.

Answer 5

As it gains speed the gravitational potential energy decreases and the kinetic energy increases.

Gravitational Potential Energy → Kinetic energy

Question 6

What is the law of conservation of energy?

Answer 6

Energy cannot be created or destroyed, it can only be transferred from one place to another or transformed from one form of energy to another

energy in = energy out

Question 7

What is wasted energy? Give and example.

Answer 7

Wasted energy is caused by unwanted energy transfer.

e. g. in a light bulb heat energy is wasted energy

Question 8

Name 10 types of energy.

Answer 8

1. Nuclear
2. Kinetic
3. Thermal
4. Sound
5. Light
6. Elastic
7. Gravitational potential
8. Chemical
9. Magnetic
10. Electrical

Question 9

How is energy dissipated by elastic objects?

Answer 9

As an elastic material stretches and compresses elastic energy is transformed to thermal energy wich is dissipated (given off) to the surroundings

Question 10

How is energy dissipated by moving objects?

Answer 10

As moving parts rub together friction causes kinetic energy is transferred to thermal energy which is dissipated to the surroundings

Question 11

Draw the energy transfer diagram for a TV.

Answer 11

Electrical → Light + Sound + Thermal

Question 12

Draw the energy transfer diagram for a petrol car

Answer 12

Chemical → Kinetic +Thermal + Sound

Question 13

Describe the changes in energy stores of an electric train as it:

a) moves up a hill
b) brakes to a halt

Answer 13

a) electric energy of train motor → Gravitational Potential Energy of train
b) friction on train wheels due to brakes reduces the kinetic energy of the train to zero → heat and sound to surroundings

Question 14

List 2 different objects you could use to light a room if you have a power cut.

Describe the energy transfer and changes to energy stores when it lights the room.

Answer 14

1. Electric torch

Chemical energy (battery) → electric energy (bulb)→ Light + Heat (into the surroundings)

2. Candle

Chemical (from burning) → heat + light (into the surroundings)

Question 15

Write the formula for

Work done =

Answer 15

Work done (J) = Force (N) x distance (m)

Question 16

Calculate how much work is done when a force of 2000N pulls a truck a distance of 40 in the direction of the force.

Answer 16

Force X distance = work doe

2000N x 40m = 80 000 J

Question 17

Alicia lifts a laptop 2 m into the air with the force of 10N. How much work does she do?

Answer 17

Force X Distance = Work done

10N x 2m = 20 J

Question 18

Write the formula for:

Gravitational Potential Energy (GPE) =

Answer 18

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

Question 19

If Sophie climbs a ladder 3.4 m tall and Sophie has a mass of 48 kg, how much GPE has she gained?

Answer 19

48 kg x 10 N/kg x 3.4 m = 1632 J

Question 20

Write the formula for:

Kinetic energy (KE) =

Answer 20

Kinetic energy = 1/2 x mass x velocity²

Question 21

Usain Bolt has a mass of 85 kg and is running at a steady speed of 10m/s. How much kinetic energy does he have?

Answer 21

1/2 x 85kg x (10m/s)² = 4250 J

Question 22

Write the formula for:

Elastic energy=

Answer 22

Elastic energy = 1/2 x spring constant x extention²

Question 23

A catapult is used to fire an object into the air. Describe the energy transfer when the catapult is:

a) stretched
b) released

Answer 23

a) work done by muscles transfer chemcial energy from muscles → elastic potenial energy of catapult
b) elastic potential energy of catapult → kinetic energy of object

Question 24

An object weighing 2.0N fired vertically upwards from a catapult reaches a maximum height of 5.0 m. Calculate the increase in gravitational potential energy store of the object

Answer 24

2.0N x 5.0m = 10 J

Question 25

A mobility aid to assist walking uses a steel spring to store energy when the walker’s foot goes down and it returns energy as the foot is lifted. The spring has a constant of 250 N/m. Calculate the elastic potential energy stored in the spring when its extension is

0.21 m.

Answer 25

1/2 x extension²x spring constant = Elastic energy

0.5 x (0.21 m)²x 250N/m = 5.5 J

Question 27

What is and independent variable?

Answer 27

The variable you can CHANGE.

Question 28

What are the control variables?

Answer 28

The variables you keep the SAME.

Question 29

What is the dependent variable?

Answer 29

The variable you MEASURE (when you change the independent variable)