Exam-style Questions: Energy Calculations

  1. A diver climbs some steps to a diving board. Which two of the statements P, Q, R, S and T are true?

    P: as the diver falls, gravitational potential energy is transferred to kinetic energy

    Q: as the diver falls, kinetic energy is transferred to gravitational potential energy

    R: the gravitational potential energy of the diver on the board is equal to the energy transferred to the diver when climbing the steps

    S: the kinetic energy of the diver on the board is equal to the energy transferred to the diver when climbing the steps

    T: when the diver hits the water, all the gravitational potential energy is regained

    (Marks available: 2)

    Answer

    Answer outline and marking scheme for question: 1

    P and R

    (Marks available: 2)

  2. The formulae below may be of help with parts of this question.

    efficiency = useful energy transferred by device

    total energy supplied to device

    The diagram shows what happens to the Sun's radiation when it falls on a panel of solar cells.

    Copyright S-cool

    a) What is the overall efficiency of the transfer of light energy from the Sun to electrical energy?

    A 15%

    B 36%

    C 71%

    D 100%

    (1 Mark)

    b) Each square metre of the solar panel receives 500 W. The area of the panel is 5m2. How much energy falls on the panel in 2 hours?

    A 5 J

    B 5000 J

    C 3,600,000 J

    D 18,000,000 J

    (1 Mark)

    c) Another panel of solar cells has an efficiency of only 6%. What is the electrical output of this panel when the input power is 2500 W?

    A 150 W

    B 417 W

    C 15,000 W

    D 1,500,000 W

    (1 Mark)

    d) In less developed countries, where fuel is unavailable and where sunshine ratings are high, solar energy is used to drive turbines. An array of mirrors tracks the Sun and focuses its heat on to a container of oil. This heats the oil to 400°C.

    How should the hot oil be used to drive the turbines?

    A The hot oil is burnt to heat water to make stem to drive the turbines

    B The hot oil flows from a high level to a low level to drive the turbines

    C The hot oil heats water, making steam which drives the turbines

    D The hot oil is pumped through the turbines

    (1 Mark)

    (Marks available: 4)

    Answer

    Answer outline and marking scheme for question: 2

    a) A

    (1 Mark)

    b) D

    (1 Mark)

    c) A

    (1 Mark)

    d) C

    (1 Mark)

    (Marks available: 4)

  3. A group of houses uses solar panels and windmills as alternative energy sources.

    a) The panels and windmills are expensive to install.

    Eventually all the money spent on them will be reocvered.

    Explain why.

    (2 Marks)

    b) Jan works out the efficiency of one of the windmills. The energy of the air hitting the blades of the windmills is 20 000 J each second.

    The energy transferred to the power lines is 5000 J each second.

    Calculate the efficiency of the windmill. Use the equation below:

    You must show how you work out your answer.

    energy efficiency = useful energy out

    total energy input

    effiency =..............................

    (2 Marks)

    (Marks available: 4)

    Answer

    Answer outline and marking scheme for question: 3

    a) panels and windmills provide free energy/ no bills/ low running costs

    (1 Mark)

    save other fuels/ payback covers initial costs

    (1 Mark)

    b) 5000/20000

    (1 Mark)

    0.25/25%

    (1 Mark)

    (Marks available: 4)