Kinetic energy, ke
4 marks · NormalA car of mass 1100 kg is travelling at 20 m/s on a motorway.
Calculate the kinetic energy of the car.
Explain what happens to this energy if the car brakes to a stop.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) 220,000 J
(b) The kinetic energy is transferred mainly to heat energy in the brakes and tyres, and some to sound. · must show mention of heat/friction, mention of transfer to surroundings
Common mistakes: Incorrectly calculating KE; Not mentioning heat from friction
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Marking points
M1 (a) · 1 mark · Correct equation and substitution for KE
A1 (a) · 1 mark · Correct final value and unit
B1 (b) · 1 mark · States energy becomes heat in the brakes
B2 (b) · 1 mark · Mentions transfer to surroundings or as sound
Worked solution
a)
b)
The car's kinetic energy is transferred to heat energy in the brakes and tyres due to friction. Some of the energy is also transferred to the surroundings as sound.