Question

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Calculate the work done by a boy lifting a 1 kg books from the floor and keeping it on a book shelf 3 metre high. ​

Answer 1

Let me assume that the only force opposing your force is gravitational force. In that case, I may write the work done as

W = F.S , where F and S are vectors, viz. dot product of Force and Displacement.

= F x S x cos(Angle between F and S ) , here F and S representing magnitudes of F ad S .

So, the angle between F and S is 0 degrees, giving us the value of cosine 1.

So, W = F x S x 1

But, as work is done against only gravitational force, the force may be taken as

F = mg = 9.8 N

And given the displacement S = 2m,

Work W = (9.8 N)(2m) = 19.6 Nm = 19.6 J

Hope it helps!