Question

A weight lifter lifted a load of 2000 kgf to a height of 2.5 m in 5 s . calculate ( i ) the work done and ( ii ) the power developed by him. Take G = 10Nkg-1

Answer 1

work done =2000*10*2.5*=50000N

power=work done/time=50000/5=10000W

Answer 2

Force acting on the body = 10kgf = 10 x 10N=100N
Displacement, S=0.5 m
Work done= force x displacement in the direction of force
(i) W =F x S
W = 100 x 0.5= 50 J
(ii) Work = force x displacement in the direction of force
W = F x S cos?
W = 100 x 0.5 cos60o
W= 100 x0.5 x 0.5 (cos60o=0.5)
W=25 J
(iii) Normal to the force:
Work = force x displacement in the direction of force
W = F x S cos?
W = 100 x 0.5 cos90o
W= 100 x 0.5 x 0 =0 J (cos90o =0)