9th grade energy

Question 1

A motor is 35% efficient. It is supplied with 3000 J. How much useful energy does it transfer, in J?

Answer J

Question 2

Nuclear power stations release very little carbon dioxide while running. What is a main disadvantage?

• A. They produce acid rain
• B. Radioactive waste must be stored safely for a very long time
• C. They cannot generate much electricity
• D. They only work when it is sunny

Question 3

A force of 150 N pushes a box 12 m along the floor. How much work is done, in J?

Answer J

Question 4

A ball is dropped from 10 m. Ignoring air resistance, all its gravitational potential energy becomes kinetic energy. How fast is it moving just before it lands, in m/s? Use g = 10 N/kg.

Answer m/s

Question 5

What is the kinetic energy of a 60 kg object moving at 10 m/s? Use Eₖ = ½ m v².

Answer J

Question 6

An object of mass 60 kg is lifted 3 m. How much gravitational potential energy does it gain? Use Eₚ = m g h with g = 9.8 N/kg.

Answer J

Question 7

A device is supplied with 200 J and transfers 160 J usefully. What is its efficiency, as a percentage?

Answer %

Question 8

A 2 kW heater is used for 10 hours. Electricity costs 15 cents (pence) per kWh. How much does it cost to run, in cents (pence)?

Answer 

Question 9

In one year a country generated 200 TWh of electricity. Renewables supplied (TWh): wind 34, solar 16, hydroelectric 20. What percentage of the electricity came from these renewables?

Answer %

Question 10

An appliance transfers 12000 J of energy in 120 s. What is its power, in watts?

Answer W

Question 11

Can a device be more than 100% efficient?

• A. Yes, if it is very small
• B. No, because energy cannot be created
• C. Yes, if it is new
• D. Yes, if it uses a battery

Question 12

Is this energy resource renewable or non-renewable: geothermal?

• A. renewable
• B. non-renewable

Question 13

A motor is 35% efficient. It is supplied with 1500 J. How much useful energy does it transfer, in J?

Answer J

Question 14

Why are large batteries and pumped hydro storage being built alongside renewables?

• A. To store surplus energy and release it when demand is high or generation is low
• B. To make renewables produce more carbon dioxide
• C. To replace transmission lines
• D. Because renewables need batteries to start

Question 15

A force of 20 N pushes a box 3 m along the floor. How much work is done, in J?

Answer J

Question 16

A ball is dropped from 45 m. Ignoring air resistance, all its gravitational potential energy becomes kinetic energy. How fast is it moving just before it lands, in m/s? Use g = 10 N/kg.

Answer m/s