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imatreyu
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Homework Statement
"You push a 325-N trunk up a 20.0 degree inclined plane at a constant velocity by exerting a 211-N force parallel to the plane's surface."
What force must be exerted on said trunk so that it would slide down the plane with a constant velocity? In which direction should the force be exerted?
Homework Equations
W=mg
Fnet= ma
I'm not really sure about this section.
The Attempt at a Solution
I drew a free body diagram with the known forces that are acting on the object (the Normal--perpendicular to the inclined plane, and the weight straight down). I also drew in the supposed pushing force and the opposing frictional force. I aligned the diagram on a coordinate plane so that all forces lie on an axis EXCEPT the weight.
I resolved the weight:
Wx= 325cos70
Wy= 325sin70
And found the coeff. of friction:
sum of all forces y-axis:
Fnet= N + Wy
Fnet= N-Wy
Fnet= 0
sum of all forces x-axis:
Fnet= Pushing force + Ff + Wx
Fnet= Fp + Wx - Ff
ma= Fp + Wx -Ff
(velocity is constant--> there is no acceleration):
0= Fp + Wx - Ff
0= 211 - (325cos70) - Ff
Ff= approximately 100 N, the coeff of friction is thus approximately .3278
I am totally stuck now, though on how to find the force needed to cause the trunk to slide down the plane with constant velocity. . . .
And I might have done something wrong above. :( Please help!
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