Question
The graph below shows the variation between force and distance for a boy pushing a concrete block of mass 25kg through a vertically height of 12m.
i) Determine the total work done by the boy within 70m
ii) How much energy is wasted?
iii) Give an account for the energy wasted
i) Determine the total work done by the boy within 70m
ii) How much energy is wasted?
iii) Give an account for the energy wasted
Answer
i)
work done = Area under the graph
= (40 x 20) + (20 x 10) = (80 x 40)
= 800 + 200 + 3200 = 4200J
ii)
work done = mgh
= 25 x 10 x 12 = 3000J
Energy wasted = (4200 - 3000)J = 1200J
(iii) Friction force between the surfaces. Some work is done against friction
work done = Area under the graph
= (40 x 20) + (20 x 10) = (80 x 40)
= 800 + 200 + 3200 = 4200J
ii)
work done = mgh
= 25 x 10 x 12 = 3000J
Energy wasted = (4200 - 3000)J = 1200J
(iii) Friction force between the surfaces. Some work is done against friction
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