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A block of mass 2 kg rests on top of a larger block of mass 8 kg,…

Question

A block of mass 2 kg rests on top of a larger block of mass 8 kg, which itself rests on a frictionless floor. The coefficient of friction between the two blocks is 0.40. A horizontal force is applied to the upper block. Taking g = 10 m/s^2, find the maximum magnitude (in newtons) of this applied force for which the two blocks still move together without relative sliding.

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Step-by-step solution

The only horizontal force on the lower block is friction from the upper block, with maximum value f_max = mu*m*g = 0.4*2*10 = 8 N.

This gives the lower block's maximum acceleration while moving together: a_max = f_max/M = 8/8 = 1 m/s^2.
Moving together, the whole system (mass 10 kg) has this acceleration when F = (m+M)*a_max = 10*1 = 10 N.

Beyond this the upper block slips.

Final answer10

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