Exam (elaborations)
A Level Physics Mechanics: Work, Energy, and power exam questions
A Level Physics Mechanics: Work, Energy, and power exam questions.
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A Level
A Level Physics
MECHANICS: Work, Energy And
Power (Answers)
Name:
Total Marks: /30
Maths Made Easy © Complete Tuition Ltd 2017
,1. To make lifting water from a well much easier, a long handle (50 cm) is attached to the axle around
which the rope is wound, as shown below. Ignore the weight of the rope.
Total for Question 1: 13
(a) State the principle of conservation of energy. [2]
Solution: The total energy of a closed system remains constant: energy may not be created
nor destroyed, but may be transferred from one form to another.
(b) By considering the work done taking a body from rest to speed v with constant acceleration, show [3]
that kinetic energy = 21 mv 2 .
2
Solution: v 2 = u2 + 2as. For u = 0, as = v2 .
Work done = F d cos θ. Here θ = 0 → cos θ = 1.
F = ma → work done = mas = 12 mv 2
Page 2
, (c) A force of 500 N must be applied to the handle’s end to lift the bucket of water, which has a combined [4]
mass of 50 kg. Given that the diameter of the winding axle is 5 cm, calculate the efficiency of the
machine.
Solution: 5 %
(d) Bethan lifts the bucket using the handle. She then lets go. Sketch on two graphs, one for time and [4]
one for distance, the form of the variation of: (a) kinetic energy with time (b) potential energy with
time (c) kinetic energy with distance (d) potential energy with distance. Assume that there are no
frictional forces and that air resistance is negligible.
Solution: (a) Quadratic dependence on t2 ; concave-up
(b) Quadratic dependence on t2 ; concave-down
(c) linear dependence on distance; positive gradient
(d) linear dependence on distance; negative gradient
Page 3
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