A block of mass 25 kg is raised by a 50 kg man in two different
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? solution:

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, $g=10 \mathrm{~m} / \mathrm{s}^{2}$

Force applied on the block, $F=25 \times 10=250 \mathrm{~N}$

Weight of the man, $W=50 \times 10=500 \mathrm{~N}$

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 $=250+500=750 \mathrm{~N}$

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 $=500-250=250 \mathrm{~N}$

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.