A taut string connects a 5-kg crate to a 12-kg crate (see figure below). The coe

Question

A taut string connects a 5-kg crate to a 12-kg crate (see figure below). The coefficient of static friction between the smaller crate and the floor is 0.573; the coefficient of static friction between the larger crate and the floor is 0.443. Find the minimum horizontal force required to start the crates in motion.

A taut string connects a 5-kg crate to a 12-kg crate (see figure below). The coefficient of static friction between the smaller crate and the floor is 0.573; the coefficient of static friction between the larger crate and the floor is 0.443. Find the minimum horizontal force required to start the crates in motion.

Explanation / Answer

1. What is the minimum horizontal force F required to start the crates in motion?
Fr1 = -(m1*g*?1s) = -(5*9.8*0.573) = -28.1 N ..resistent force of small crate
Fr2 = -(m2*g*?2s) = -(12*9.8*0.443) = -52.1 N..resistent force of large crate
Motive force Fm = -(Fr1+Fr2) = -(-28.1-52.1) = 80.2 N ..total required motive force

2. What is the tension in the rope when that force is applied?
T = -Fr2 = -(-52.1) = 52.1 N

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