Question

(a) A horizontal force of 100 N is used to push a 20 kg box 10 meters across a level. How much work we have to do? (b) How much work is needed to raise the same box by 10 m?

Answer 1

Given

the applied force F = 100 N

mass of the box is m = 20 kg,

displacement is s = 10 m

work done by the force on the box is W = ?

by the definition of work doe W = F . S = F*S cos theta

here theta is zero both the displacement and force are in the same direction so cos 0 = 1

a)

   W = F*s

   W = 100*10 J = 1000 J

work done W = 1000 J

b) to raise the same box to a heigh of h =1 0 m , the work must be done is

equal to the gravitational potential energy attained by the box at height 10 m

that is by conservation of energy work done on the box = gravitatioanal potential energy

   W = m*g*h

   W = 20*9.8*10 J

   W = 1960 J

so the work is needed to raise the same box by 10 m is 1960 J