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A block of mass 25 kg is raised by a 40 kg man in two different cases as shown in the figure.
1. Action on the floor by the man in fig (a) is
______ N.
(a)150
(b)400
(c)250
(d)650
(ii) Action on the floor by the man in fig (b) is
______ N.
(a)150
(b)400
(c)250
(d)650
Answers
Explanation:
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=25×10=250N
Weight of the man, W=50×10=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.