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?

What is the action on the floor by the man in the two cases

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.
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