Question

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?

Answer 1

750 N and 250 N in the respective cases; Method (b)
Mass of the block, m = 25 kg
Mass of the man, M = 50 kg
Acceleration due to gravity, $g=10m/s^2$
Force applied on the block, $F=25\times 10=250N$
Weight of the man, $W=50\times 10=500N$

Case (a): When the man lifts the block directly
In this case, the man applies a force in the upward direction. This increases his apparent weight.
$\therefore$ Action on the floor by the man = 250 + 500 = 750 N

Case (b): When the man lifts the block using a pulley
In this case, the man applies a force in the downward direction. This decreases his apparent weight.
$\therefore$ Action on the floor by the man = 500 - 250 = 250 N
If the floor can yield to a normal force of 700 N, then the man should adopt the second method to easily lift the block by applying lesser force.