A block of mass 25 kg is raised by a 50 kg man in two different ways as shown in Fig. 5.19. What is the action on the floor by the man in the two cases ? If the floor yields to a normal force of 700 N , which mode should the man adopt to lift the block without the floor yielding ?

Explanation

In mode (a) , the man applies a force equal to 25 kg weight in upward direction. According to Newton's third law of motion, there willl be a downward force of reaction on the floor.

`therefore` Total action on the floor by the man
=50kg wt+25 Kg wt
=75 kg wt
=75xx9.8 N
=735 N
In mode (b) the man applies a downward force on ropes equal to 25 kg wt. According to Newton's third law, the reaction will be in the upward direction by the ropes on the man so be becomes light by 25 kg wt.
`therefore` Total action on the floor by the man
=50 kg wt-25 kg wt
=25 kg wt =`25xx9.8 N`=245 N
As the floor yields to a downward force of 700 N, so the man should adopt mode (b).