Question

Two crates, of mass 65 kg and 125 kg, are in contact and at rest on a horizontal surface. A 650-N force is exerted on the 65-kg crate. If the coefficient of kinetic friction is 0.18, calculate the force that each crate exerts on the other.

Answer 1

Determine do they accelerate ?
weight = m g = (65+125)(9.8) = 1862 N
so kinetic friction = .18*1862 = 335 Newtons
so
a = (650-335)/(190) = 1.66 N/m^2
Force on big crate from little crate - 0.18*125*9.8 = 125*1.66
so F on big = 207.5+ 220.5 = 428 N
OR
just say F = [125/(125+65) ]* 650 = 438 N

Answer 2

typo 428 N

Answer 3

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