34.  In the figure shown, the friction coefficient between the block of mass 1 kg and plank of mass 2 kg is 0.4 while that between the plank and floor is 0.1.  a constant force F start acting horizontally on the upper 1 kg block.  The acceleration of plank if F = 10 N is
A )     10 3 m / s 2           B )     7 3 m / s 2                     C )     0 . 5   m / s 2                 D )     1 . 0   m / s 2

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1)  Limiting friction on the plank by the ground which is in backward direction  is f1=μ1N1=0.1×3×10=3N2)Limiting friction on the upper surface of the plank which acts on it in the forward direction is by the block is f2=μ2N2=0.4×1×10=4N3)Net force on the plank in the forward direction is Fnet=4-3=1ma=1a=12=0.5m/s2Regards

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