A bus filled with passengers has a mass of 3000 kg. Travelling at a steady speed of 60 km.hr-1, it overcomes frictional forces amounting to 1/200 the weight of the bus. What power does the engine of the bus put out? (g = 9.80 m.s-2.)
A bus filled with passengers has a mass of 3000 kg. Travelling at a steady speed of 60 km.hr-1, it overcomes frictional forces amounting to 1/200 the weight of the bus. What power does the engine of the bus put out? (g = 9.80 m.s-2.) |
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The speed of the bus is 60 km.hr-1, or 16.7 m.s-1.
The frictional forces that are overcome are (3000 x 9.80 ÷ 200) = 147 N.
The work done per second, that is the power P, will be the frictional force, F multiplied by the distance, s, travelled in that second, namely Fs.
P = Fs = 147 (N) x 16.7 (m) ÷ 1 (s) = 2455 W = 2.5 kW.
