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Question:

A body of mass 40kg resting on a rough horizontal surface is subjected to a force 'P' which is just enough to start the motion of the body. If μs=0.5, μk=0.4, g=10m/s² and the force 'P' is continuously applied on the body, then the acceleration of the body is

1m/s2

2m/s2

Zero

2.4m/s2

Solution:

Since P is the force which is just enough to start the motion of the body, P = μsN = μsmg
When the body moves under this force, the net force on the body is given by
F = ma = P - f
⇒ ma = μsmg - μkN = m(μs - μk)g
⇒ a = (μs - μk)g = (0.5 - 0.4)(10) m/s²
⇒ a = 1 m/s²