| The diagram shows a cyclist moving down a small hill at P before travelling on a flat road at Q. The total mass of the cyclist and his bicycle is 60 kg and the speed of the cyclist at P is\[10\text{ m}{{\text{s}}^{-1}}\]. |
| Which of the following is incorrect? |
|
A) The kinetic energy at P is 3000 J.
B) The loss of gravitational energy between P and Q is 1800 J.
C) Total energy is 4800 J.
D) The cyclist does not require a greater power when he travels at a higher constant speed.
Correct Answer: D
Solution :
(A) \[K=\frac{1}{2}\times 60\times 10\times 10=3000J\] (B) \[\text{PE = 60}\times \text{10}\times \text{3 =1800 J}\] (C) Total energy = KE + Loss of gravitational potential energy = 3000 + 1800 = 4800 J (D) The air resistance is higher when he travels at a higher constant speed, so a higher rate of work is done against air resistance. \[\therefore \] Higher power is required.
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