A block of mass 25 kg is raised by a 50 kg man in two different ways as shown in figure. 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

Here, mass of block m = 25 kg
Mass of man M = 50 kg
Force applied to lift the block or tension in string is
`T=mg = 25xx9.8 = 245 N`
Weight of Man `W=mg = 50xx9.8=490 N`
(a) When block is raised by man as shown in figure (a), force is applied by the man in the upward direction.
Thisincreases the apparent weight of the man. Hence reaction of the floor on the man or apparent weight of man or action on the floor is
R (or) `W^(1)=W+T=490+245=735 N`
(b) When block is raised by man as shown in figure (b), force is applied by the man in the downward direction. This decreases the apparent weight of the man. Hence reaction of the floor on the man or apparent weight of man or action on the floor is
`W^(1)=W-T=490-245=245 N`
As the floor yields to a normal force of 700 N, the mode (b) has to be adopted by the man to lift the block.