Page 96 - Physics Coursebook 2015 (A level)

Cambridge International AS Level Physics
6 A cyclist pedals a long slope which is at 5.0° to the horizontal (Figure 5.21). The cyclist starts from rest at the top of the slope and reaches a speed of 12 m s−1 after a time of 67 s, having travelled 40 m down the slope. The total mass of the cyclist and bicycle is 90 kg.
40 m
5.0°
Figure 5.21 For End-of-chapter Question 6.
a Calculate:
i the loss in gravitational potential energy as he travels down the slope [3]
ii the increase in kinetic energy as he travels down the slope. [2]
8 a
vertical pole, if there is a constant force of friction acting on him. [2] ii The man slides down the pole and reaches the ground after falling a distance h = 15 m. His
potential energy at the top of the pole is 1000 J. Sketch a graph to show how his gravitational
potential energy Ep varies with h. Add to your graph a line to show the variation of his kinetic
energy Ek with h. [3]
Use the equations of motion to show that the kinetic energy of an object of mass m moving with
9 a
i Calculate the average power used to accelerate the car in the first 6.0 s. [2] ii The power passed by the engine of the car to the wheels is constant. Explain why the
acceleration of the car decreases as the car accelerates. [2]
i Define potential energy. [1]
Use your answers to a to determine the useful power output of the cyclist. [3] Explain what is meant by work. [2]
Explain how the principle of conservation of energy applies to a man sliding from rest down a
b i
ii Suggest one reason why the actual power output of the cyclist is larger than your value in i. [2]
7 a
b i
velocity v is 12 mv2. [2] b A car of mass 800kg accelerates from rest to a speed of 20ms−1 in a time of 6.0s.
ii Distinguish between gravitational potential energy and elastic potential energy. [2] b Seawater is trapped behind a dam at high tide and then released through turbines. The level
of the water trapped by the dam falls 10.0 m until it is all at the same height as the sea.
i Calculate the mass of seawater covering an area of 1.4 × 106 m2 and with a depth of 10.0 m.
(Density of seawater = 1030 kg m−3) [1]
ii Calculate the maximum loss of potential energy of the seawater in i when passed through
the turbines. [2]
iii Thepotentialenergyoftheseawater,calculatedinii,islostoveraperiodof6.0hours.
Estimate the average power output of the power station over this time period, given that
the efficiency of the power station is 50%. [3]
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