P2.2 - Energy

Question 1

What is the unit of energy?

Answer 1

Joules (J)

Question 2

How many joules are there in a kilojoule(kJ)?

Answer 2

1000J

Question 3

Calculate how far you would need to run to burn off 50g of chocolate using the information given below.

On average a person can run 150m per minute.
Chocolate has 1500kJ of energy per 100g.
60kJ of energy is burnt off for each minute of running.

Answer 3

50g of chocolate = 1500kJ ÷ 2
                              = 750kJ
Run time = 750 kJ ÷ 60kJ
                = 12.5mins
12.5mins x 150m = 1875m

Question 4

State the law of conservation of energy.

Answer 4

Energy cannot be created or destroyed. It can only be transferred.

Question 5

There are 5 main different types of energy stores. What are they?

Answer 5

Chemical - food, batteries, fuels
Gravitational Potential - position in a gravitational field
Kinetic - moving objects
Elastic - stretching or changing shape
Thermal - hot objects

Question 6

What is meant by a good conductor of energy?

Answer 6

Energy is transferred through it quickly.

Question 7

What are the three ways that energy can be transferred by.

Answer 7

Conduction
Convection
Radiation

Question 8

What is conduction.

Answer 8

Particles transfer energy by colliding with each other when they vibrate.

Question 9

Are gases good conductors

Answer 9

They are not.

Question 10

What is a convection current?

Answer 10

Liquid is heated up at a lower section making the particles vibrate. The particles in the liquid move further apart making it less dense. The less dense liquid moves up and the denser colder liquid takes its place.

Question 11

What does radiation travel as?

Answer 11

Waves.

Question 12

Does radiation need air to transfer energy?

Answer 12

No. Radiation can be transferred without particles. An example is the sun and how there are no particles in space.

Question 13

Would a dark blue shirt absorb more or less infrared radiation than a white shirt.

Answer 13

It would absorb more radiation. Dark colours absorb more while light or shiny things would reflect more.

Question 14

Do animals emit infrared radiation? If so what animals would emit a normal amount and what animals would emit close to none.

Answer 14

Most animals emit infrared radiation including humans. A snake would not emit much infrared radiation as it is cold blooded.

Question 15

A power rating tells you how much energy is transferred per second.
What is the equation to calculate power (W)?

Answer 15

power (W) = energy (J) / time (s)

Question 16

How do you calculate work done (J)?

Answer 16

work done (J) = force (N) / distance (m)