question_answer 31)

A block of mass 25 kg is raised by a 50 kg man in two different ways as shown in Fig. 5.133. 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 ? (a)                          (b) Fig. 5.133  

Answer:

In mode (a), the man applies force equal to 25 kg wt in the upward direction. According to Newton's third law of motion, there will be a downward force of reaction on the floor.  Total action on the floor by the man   . In mode (b), the man applies a downward force equal to 25 kg wt. According to Newton's third law, the reaction will be in the upward direction.                          . As the floor yields to a downward force of 700 N, so the man should adopt mode (b).