Laws of MotionHard

Question

The pulley arrangements shown in figure are identical, the mass of the rope being negligible. In case I, the mass m is lifted by attaching a mass 2m to the other end of the rope. In case II, the mass m is lifted by pulling the other end of the rope with a constant downward force F = 2mg, where g is acceleration due to gravity. The acceleration of mass in case I is:

Options

A.zero
B.more than that in case II
C.less than that in case II   
D.equal to that in case II

Solution


T1 − mg = ma1            [Newton′s II law for m]
2 mg − T1 = 2 ma1        [Newton′s II law for 2m]
⇒    a1 = g/3
Case 2

F − mg = ma2            [Newton′s II law for m] 
⇒     2 mg − mg = ma2     ⇒    a2 = g       ⇒    a2 > a1

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