- #1
Johnson1704
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Homework Statement
You are lowering two boxes, one on top of the other, down the ramp shown in the figure (Figure 1) by pulling on a rope parallel to the surface of the ramp. Both boxes move together at a constant speed of 19.0 cm/s . The coefficient of kinetic friction between the ramp and the lower box is 0.457, and the coefficient of static friction between the two boxes is 0.818.
2. Questions
A What force do you need to exert to accomplish this?
B What is the magnitude of the friction force on the upper box?
3. Relevant equations
X forces: Fpull - Ffr - Fg*sin(theta) = 0
Y forces: Fn - Fg*cos(theta) = 0
Ffr = mu_k * Fn
The Attempt at a Solution
(A)[/B]I found theta to be 27.76
Ffr = mu_k * [Fg*cos(theta)]
Ffr = 317.0513 N
Fpull = Ffr + Fg*sin(theta) = 6782.214 N
The solutions I've seen on this forum say to use -Fgsin(theta) but i don't see why it would be negative. I've checked my work so many times
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