A plank of mass m 1 = 8 kg with a bar of mass m 2 = 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

Question

A plank of mass m 1 ​ = 8 kg with a bar of mass m 2 ​ = 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 m 1 ​ and m 2 ​ . 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:-

TestHub · Accepted Answer

Lift FBD in reference frame of the lift $a_{2} = \frac{1}{5} (g + \frac{g}{4}) = \frac{g}{4} = 2.5 m / s^{2}$ $a_{8} = \frac{30 - [ μ .2 ( g + \frac{g}{4} ) ]}{8} = \frac{30 - [ \frac{1}{5} \times 2 \times \frac{50}{4} ]}{8} = \frac{25}{8} m / s^{2}$

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