FrictionMedium

Question

A plank of mass m1 = 8 kg with a bar of mass m2 = 2 kg placed on its rough surface, lie on a smooth floor of elevator ascending with an acceleration g/4. The coefficient of friction is μ = 1/5 between m1 and m2. A horizontal force F = 30 N is applied to the plank. Then the acceleration of bar and the plank in the reference frame of elevator are:

Options

A.3.5 m/s2, 5 m/s2
B.5 m/s2, 50/8 m/s2
C.2.5 m/s2, 25/8 m/s2
D.4.5 m/s2, 4.5m/s2

Solution

(C)     Solving from the frame of elevator
geff. = g + g/4 = 12.5

f = × 2 × 12.5 = 5N
a2 = = 2.5 m/s2
a1 = m/sec2

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