Trunk up an Incline

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bartman
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Homework Statement


A trunk of mass m = 1.8 kg is pushed a distance d = 62 cm up an incline with an angle of inclination θ = 24.0° by a constant horizontal force P = 375 N (see figure). The coefficient of kinetic friction between the trunk and the incline is 0.19.
Figure: img144.imageshack.us/img144/8295/prob13ani7.gif

A) Calculate the work done on the trunk by the applied force P.
B) Calculate the work done on the trunk by the frictional force.
C) Calculate the work done on the trunk by the gravitational force.


Homework Equations


sin θ = y/h
cos θ = x/h
N*μk=Fk

The Attempt at a Solution


A)
cos(θ)*F*h
cos(24°)*375N*0.62m = 212J

B)
N*μk=Fk
(sin(24°)*375N + cos(24°)*1.8kg*9.8m/s/s)*.62m*.19 = 19.9J

C)
This is where I am having problems.
 

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Answers and Replies

  • #2
PhanthomJay
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Hi, Bartman, welcome to PF!

The work done by a force is equal to the product of the force times the displacement in the direction of the force ((F)(d)(cos theta)), where theta is the angle between the force and the displacement, and which can result in a positive or negative value. In part B, is the work done by friction positive or negative? In part C, the work done by the gravitational force is the work done by the trunk's weight. What is the displacement of the trunk in the direction of its weight? Is the work done by gravity positive or negative?
 

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