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Laws of Motion

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Physics Part I

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Physics

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CBSE Gujarat Board Haryana Board

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Class 10 Class 12
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?


Given,

Mass of the block, m = 25 kg

Mass of the man, M  = 50 kg 

Acceleration due to gravity, g = 10 m/s

Force applied on the block, F = 25 × 10

                                      = 250 N 

Weight of the man, W = 50 × 10 = 500 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 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. 

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