a) Why are cars made with bumpers that can be pushed in during a crash? (5)
b) A crane operated by an electric motor has a mass of 500 kg. It raises a load of 300 kg
vertically at a steady speed of 0.2 ms−1
. Assume resistance to be constant at 1200 N.
What is the power required to raise the load? (5)
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A] The cars have the bumpers with a larger surface area and this is because it leads to less impact of force by anything in opposite direction. If it is not so, the impact would be more causing some destruction in car.
B] Energy = F.s = m.a.s
Power = E/t = m.a.s/t = m.a.v (a=g=10m/s)
Total Power of crane = (500+300)(0.2)(10) = 1600W
Power of Resistance = 1200(0.2)(10) = 2400W
So, the power required to raise the load = 2400-1600 = 800W
B] Energy = F.s = m.a.s
Power = E/t = m.a.s/t = m.a.v (a=g=10m/s)
Total Power of crane = (500+300)(0.2)(10) = 1600W
Power of Resistance = 1200(0.2)(10) = 2400W
So, the power required to raise the load = 2400-1600 = 800W
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