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A block of mass m1 = 4.50 kg sits on top of a second block of mass m2 = 13.9 kg, which in turn is on a horizontal table. The coefficients of friction between the two blocks are µs = 0.300 and µk = 0.100. The coefficients of friction between the lower block and the rough table are µs = 0.500 and µk = 0.400. You apply a constant horizontal force to the lower block, just large enough to make this block start sliding out from between the upper block and the table.
Determine the magnitude of each force on each block at the instant when you have started pushing but motion has not yet started. In particular, what force must you apply?

I tried finding the applied force using:
Fa = µs (m2g) + µs (m1g)
Fa = .5(13.9 x 9.8) + .3(4.5 x 9.8)= 81.34 N. This was not correct. Any suggestions?

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