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You are lowering two boxes, one on top of the other, down the ramp shown in Figure 5.53 by pulling on a rope parallel to the surface of the ramp. Both boxes move together at a constant speed of 15.0 cm/s. The coefficient of kinetic friction between the ramp and the lower box is 0.444, and the coefficient of static friction between the two boxes is 0.800. (a) What force do you need to exert to accomplish this? (b) What are the magnitude and direction of the friction force on the upper box?

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Equations

(2)w = mg

(1)F = uk(m1+m2)g+us*m2g

Solution:

Well i added the two boxes masses to 80 kg and i got the angle to be 27.7 degrees

(1)w = m(tot)*g = 784,8 N

(2)F = uk(m1+m2)g +us*m2*g <==>

F = 599.4 N

The answer should be 57.1 N