5.32 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?
Fig. 5.19
Given,
mass of the block, m = 25 kg
Mass of man, M = 50 kg
Force applied to lift the block,
F = mg = 25 x 10 = 250 N.
Weight of man, W = Mg = 50 x 10 = 500 N
1. When block is raised by man as shown in figure (a), force is applied by the man in the upward direction. Action on the floor by the man = W-F = 500 + 250 = 750 N
2. When block is raised by man as shown in figure (b), force is applied by the man in the downward direction.
Action on the floor by the man
= W-F = 500 – 250 = 250N
As the floor yields to a normal force of 700 N, model (b) has to adopted by the man to lift the block.
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