Conservation Of Energy Problem

1. Nov 17, 2005

leolaw

So this is the quaiton that i have problem w/:
A 4kg bundle starts up a 30 degree incline with 128J of kinetic energy. How far willl it slide up the incline if the coefficient of kinetic friction between bundle and incline is 0.3?

Because E_initial + Work = E_final and the Work done in the system in this problem is jsut the fricition force, so I have
128 + $$\mu$$F_f = 0
128 - $$\mu$$mg cos $$\theta$$ d = 0

since that d is what we are looking for, rearranging this equation gives me:
128 / ($$\mu$$mg cos $$\theta$$) = d

and d = 12.6m

however, the answer is 4.3m, did I mess up any steps above?

Last edited: Nov 17, 2005
2. Nov 18, 2005

Staff: Mentor

Don't forget that gravity also does work on the object. (Or, alternatively, make sure that energy includes both kinetic and gravitational PE.)