General Physics 1.7 Energy, Work & Power

Question 1

What type of energy is stored in a moving object?

Answer 1

Kinetic energy.

Question 2

What happens, in terms of energy, when an object is lifted?

Answer 2

Its gravitational potential energy increases.

Question 3

Give an equation for kinetic energy

Answer 3

kinetic energy (J) = ½ × mass (kg) × velocity^2 (m/s)
E = ½mv^2

Question 4

Give an equation for gravitational potential energy

Answer 4

Gravitational potential energy (J) = mass (kg) x
height (m) x gravitational field strength (N/kg)
E = mgh

Question 5

When work is done against friction or resistance, what happens?

Answer 5

There is less of a change in kinetic energy because some energy is dissipated through heating.

Question 6

What is the original source of most of the energy on Earth?

Answer 6

The sun.

Question 7

What forms of energy do not ultimately come from the sun?

Answer 7

• Geothermal
• Nuclear
• Tidal

Question 8

What is the source of the sun’s energy?

Answer 8

Nuclear fusion.

Question 9

What are the main energy resources available to humans?

Answer 9

Fossil fuels (oil, gas and coal), nuclear fuels, biofuels, wind, hydroelectricity, tides and solar energy.

Question 10

Define renewable energy.

Answer 10

Energy from a source which does not run out, so can be replenished.

Question 11

Which energy sources are non-renewable?

Answer 11

• Fossil fuels
• Nuclear fuel

Question 12

Which energy sources are renewable?

Answer 12

• Biofuels
• Wind
• Hydroelectric and tidal energy
• Geothermal energy
• Solar power

Question 13

Why is non-renewable energy used to provide electricity on a large scale?

Answer 13

Non-renewable sources tend to have a larger energy output per kilogram of fuel.

Question 14

What is efficiency?

Answer 14

The ratio of useful work done to energy supplied, often given as a percentage, i.e. the percentage of energy which is converted to a useful form.

Question 15

Give the equation for efficiency

Answer 15

Efficiency =Useful energy output / Total energy input
You can convert this to a percentage by multiplying the answer by 100.

Question 16

How can the efficiency of a system be increased?

Answer 16

1. Reducing waste output (by lubrication, thermal insulation etc.)
2. Recycling waste output (eg. recycling thermal waste energy as input energy)

Question 17

Define work done.

Answer 17

• Work is done on an object when energy is transferred (from one form to another)
• Equal to the product of force and distance

Question 18

Give the equation for work done

Answer 18

work done (J) = force (N) × distance (m)
W= Fd
(where distance is the distance moved along the line of action of the force)

Question 19

Define power.

Answer 19

Power is the rate at which energy is transferred or the rate at which work is done.

Question 20

Give 2 equations for power

Answer 20

power (W) = energy (J) ÷ time (s)
power (W) = work done (J) ÷ time (s)