Block on a ramp problem - energy

[Marioqwe]

Homework Statement

Package is projected 10 m up a 15º incline so that it justreaches the top of the incline with zero velocity. μk =0.12

a) Determine initial velocity of package at A

Homework Equations

Energy and friction equations

The Attempt at a Solution

Height at the top of ramp h = 2.588m

Work = change in energy

W = -μmgcos(15) - mgsin(15) = mgh - 0.5mv^2

But I get the wrong answer. Am I supposed to use potential energy? and if not why not?

Thanks

 

[Doc Al]

W = -μmgcos(15) - mgsin(15) = mgh - 0.5mv^2

But I get the wrong answer. Am I supposed to use potential energy? and if not why not?

(1) If you include potential energy, that automatically takes care of the work done by gravity. Don't count it twice.
(2) The work terms must be of a form force*distance. You left out the distance.

 

[Marioqwe]

I see my mistake. many thanks Doc Al.