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CAIE A-Level Physics 5.1 Energy Conservation

Practise connecting work, energy conservation, efficiency and power in mechanical calculations, including P = W/t and P = Fv.

Syllabus
2028–2030
Course
Physics 9702
Level
AS

Exam points

  • calculate work done from the component of force along displacement and use it in energy-transfer problems
  • apply conservation of energy to relate work, energy transfers and losses in mechanical systems
  • calculate efficiency and power from energy, work and time, including P = W/t and P = Fv

Covered syllabus points

5.1.1—The concept of work, and recall and use work done = force × displacement in5.1.2—The principle of conservation of energy5.1.3—That the efficiency of a system is the ratio of useful energy output5.1.4—The concept of efficiency to solve problems5.1.5—Power as work done per unit time5.1.6—P = W / t5.1.7—P = Fv and use it to solve problems

5.1 Energy conservation question 1

[Maximum number: 3]

Question (a)

(a)

A child's toy uses the spring in (a) to launch a ball of mass 0.020 kg vertically into the air. The ball is initially held against one end of the spring which has a compression of 0.045 m . The spring is then released to launch the ball. The kinetic energy of the ball as it leaves the toy is 0.72 J .

[ 1 ]

Question (i)

(i)

The toy converts the elastic potential energy of the spring into the kinetic energy of the ball. Use the information in (a)(ii) to calculate the percentage efficiency of this conversion.

[ 1 ]

Question (b)

(b)

The ball in (b) leaves the toy at point A and moves vertically upwards through the air. Point B is the position of the ball when it is at maximum height h above point A , as illustrated in Fig. 3.2.

Fig. 3.2 (not to scale)

Fig. 3.2 (not to scale)

The gravitational potential energy of the ball increases by 0.60 J as it moves from A to B .

[ 2 ]

Question (i)

(i)

Determine the average force due to air resistance acting on the ball for its movement from A to B.
average force = N

[ 2 ]

5.1 Energy conservation question 2

[Maximum number: 1]

Another parcel is accidentally released from rest by a different aircraft when it is hovering at a great height above the ground. Air resistance is now significant.

Describe the energy conversion that occurs when the parcel is falling through the air at constant (terminal) speed.

5.1 Energy conservation question 3

[Maximum number: 1]

Which statement about efficiency is correct?

A

Efficiency does not have a unit.

B

The joule is a unit of efficiency.

C

The metre is a unit of efficiency.

D

The watt is a unit of efficiency.

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