What will be the work done by Coolie when he raises a load against the force of gravity?
Answers
Answer:
Now the mathematical equation for work done is given as
W = F . S = F.S. cos(theta) where (theta) is the angle between force and displacement.
The force applied is at 90 degree to the displacement. In this situation (theta) = 90 and cos(theta) = 0. Hence work done W = FSx0 = 0. Hence no work done.
Now the situation for a coolie under the action of gravity terms is exactly like the second case. The cooolies has to apply force to push the weight (Force) in the upward direction and has to move (displacement) in the perpendicular direction. Hence his work done is zero.
So under the condition that the collie is moving horizontally only his work done would come out to be zero.
The total work done by a coolie is as follows.
Work (coolie) = Work (gravitation) + Work (friction)
Explanation:
Work(coolie) = Work(gravity) + Work(friction)
Work(gravity) = F.S. cos(theta)
Since theta = 0 therefore Work(gravity) = 0.(This is what is given in books)
Weight of coolie + Weight on his head = (60+15) kg x 10 m/sq.s = 750 N (g = 10 m/sq.s approx)
Force of friction = mu x weight = 0.8x 750 N = 600 N approx = 600 N
This means to walk the coolie needs to exert a force of at least 600 N on the ground to move ahead.
Work(friction) = Force x Displacement
= 600 N x 250 m = 15000 J.
So the work done by a coolie is actually
Work(coolie) = Work(gravity + Work(friction)
= 0 + 15000 J
Hence the total work done is not zero but 15000 J.
This means the books teach you only about Gravitational work done and nothing else. Hence never ever tell a coolie that he has done no work.