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 ? [NCERT) om lo noi super KOLMASA 25kg 25kg

JEE/Engineering Exams

Physics

Solution

152

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( 750 mathrm{N} ) and ( 250 mathrm{N} ) in the respective cases; Method (b) Mass of the block, ( m=25 mathrm{kg} ) Mass of the man, ( M=50 mathrm{kg} ) Acceleration due to gravity, ( mathrm{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 mathrm{N} ), then the man should adopt the second method to easily lift the block by applying lesser force.