Work on a box

  • #1

Homework Statement


A trunk of mass m = 2.3 kg is pushed a distance d = 187 cm up an incline with an angle of inclination q = 18.0° by a constant horizontal force P = 225 N (see figure). The coefficient of kinetic friction between the trunk and the incline is 0.22. Calculate the work done on the trunk by the applied force P.

Calculate the work done on the trunk by the frictional force.

[PLAIN]http://img706.imageshack.us/img706/9623/prob13a.gif [Broken]


Homework Equations


work=F*D
Fk=Fn*Uf

The Attempt at a Solution



I solved for the work of the push, for the work of friction im doing this

.22*2.3*9.81*cos(18)=4.72N
4.72N*1.87m=8.83 J, and because the work is on the negative direction of the movement its -8.83.

Keeps saying my answer is wrong.
 
Last edited by a moderator:

Answers and Replies

  • #2
38
0
A simple mistake. You're doing it all correctly, and you're going to hate this. You simply forgot to consider the component of P that is perpendicular to the ramp when calculating the frictional force. =/
 

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