Energy Changes in a System Practice Questions

As the swimmer climbs the steps, which energy store of the swimmer increases?

Tick (✓) one box.

• elastic potential
• gravitational potential
• kinetic
• nuclear

Write down the equation which links gravitational potential energy $E_p$, mass $m$, gravitational field strength $g$ and height $h$.

The swimmer steps off the board and falls towards the water.

Describe the change in the way energy is stored as the swimmer falls.

State what is meant by the specific heat capacity of a substance.

Which material in the table needs the least energy to raise the temperature of $1\ \mathrm{kg}$ of the material by $1\ ^{\circ}\mathrm{C}$?

Calculate the energy needed to raise the temperature of $2.0\ \mathrm{kg}$ of copper by $10\ ^{\circ}\mathrm{C}$.

Energy = ..................................... J

Write down the equation which links power $P$, energy transferred $E$ and time $t$.

The motor transfers $96\,000\ \mathrm{J}$ of energy in $40\ \mathrm{s}$.

Calculate the power of the motor.

Power = ..................................... W

A second lift motor raises the same lift through the same height, transferring $96\,000\ \mathrm{J}$ in only $25\ \mathrm{s}$.

Calculate the power of the second motor.

Power = ..................................... W

Calculate the kinetic energy of the moving football.

Kinetic energy = ..................................... J

The goalkeeper catches the ball and brings it to rest.

Describe what happens to the kinetic energy of the ball.

Complete the sentence.

Energy can be transferred usefully, stored or dissipated, but it cannot be .......................... or ...........................

A cyclist puts oil on the chain of her bicycle.

Explain how this reduces unwanted energy transfers.

Calculate the elastic potential energy stored in the stretched spring.

Elastic potential energy = ..................................... J

The person now stretches the same spring by $0.50\ \mathrm{m}$.

Show, by calculation, that the energy stored in the spring is four times greater than in part (a).

During the night, $480\,000\ \mathrm{J}$ of energy is transferred to the concrete.

Calculate the increase in temperature of the concrete.

Temperature increase = ..................................... °C

The specific heat capacity of copper is $385\ \mathrm{J/kg\ ^{\circ}C}$.

Explain why concrete is a better choice than copper for the blocks inside a storage heater.

Other than the time for which the heater was switched on, state two quantities the student had to measure to determine the specific heat capacity of the aluminium.

Calculate the specific heat capacity of aluminium given by the student's results.

Specific heat capacity = ..................................... J/kg °C

The accepted value for the specific heat capacity of aluminium is $900\ \mathrm{J/kg\ ^{\circ}C}$.

Explain why the student's value is higher than the accepted value.

Calculate the height through which the beam was lifted.

Height = ..................................... m

The crane took $20\ \mathrm{s}$ to lift the beam.

Calculate the useful output power of the crane.

Useful output power = ..................................... W

Calculate the efficiency of the drill.

Give your answer as a percentage.

Efficiency = ..................................... %

State what happens to the remaining $180\ \mathrm{W}$.

A different drill has an efficiency of $0.85$ and a useful power output of $510\ \mathrm{W}$.

Calculate the total power input to this drill.

Total power input = ..................................... W

Suggest one way of increasing the efficiency of a drill.

Calculate the energy transferred to the thermal energy store of the surroundings.

Energy = ..................................... J

Calculate the efficiency of the engine.

Efficiency = .....................................

Use Figure 1 to explain what is meant by energy being 'dissipated'.

Which house will cool down more slowly?

Explain your answer using the information in the table.

Suggest one other change that could be made to a house to reduce its rate of cooling.

State the independent variable in this investigation and give one variable the student must control.

Which material is the best thermal insulator?

Use data from the table to justify your answer.

Suggest one improvement the student could make to this investigation.

A ball is thrown vertically upwards.

Describe the changes in the way energy is stored from the moment the ball leaves the hand until it reaches its highest point.

A car is travelling along a level road. The driver brakes and the car slows down to a stop.

Describe the changes in the way energy is stored as the car slows down.

State what is meant by a closed system.

Calculate the decrease in the gravitational potential energy of the rider.

Decrease in gravitational potential energy = ..................................... J

$20\%$ of the energy from the rider's gravitational potential store is transferred to thermal energy stores by friction and air resistance.

Calculate the speed of the rider at the bottom of the zip wire.

Speed = ..................................... m/s

Give one reason why a rider's actual speed at the bottom may be less than the value calculated in part (b).

Calculate the elastic potential energy stored in the stretched spring.

Elastic potential energy = ..................................... J

Assume that all of the energy stored in the spring is transferred to the kinetic energy store of the ball.

Calculate the speed of the ball as it leaves the launcher.

Speed = ..................................... m/s

The launcher is now pointed vertically upwards.

Assuming there is no air resistance, calculate the maximum height reached by the ball.

Maximum height = ..................................... m

Calculate the energy transferred to the thermal energy store of the water.

Energy = ..................................... J

Calculate the total energy supplied to the kettle in $120\ \mathrm{s}$.

Energy = ..................................... J

Calculate the efficiency of the kettle.

Give your answer as a percentage to 2 significant figures.

Efficiency = ..................................... %

Suggest one reason why the efficiency of the kettle is less than $100\%$.

Calculate the gravitational potential energy of the ball before it is dropped.

Gravitational potential energy = ..................................... J

Assume that air resistance can be ignored.

Calculate the speed of the ball just before it hits the floor.

Speed = ..................................... m/s

Calculate the efficiency of the energy transfer during the bounce.

Efficiency = .....................................

Explain what has happened to the rest of the energy.