Question

A block of mass $25$ $kg$ is raised by a $50$ $kg$ man in two different ways as shown in figure 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, $M=50kg$

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.

Action on the floor by the man $=250+500=750N$

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.

Action on the floor by the man $=500-250=250N$

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.