• Support PF! Buy your school textbooks, materials and every day products Here!

Block on a ramp problem - energy

  • Thread starter Marioqwe
  • Start date
  • #1
68
4

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
 

Answers and Replies

  • #2
Doc Al
Mentor
44,940
1,201
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.
 
  • #3
68
4
I see my mistake. many thanks Doc Al.
 

Related Threads on Block on a ramp problem - energy

Replies
4
Views
4K
Replies
8
Views
2K
Replies
5
Views
17K
Replies
12
Views
1K
  • Last Post
Replies
5
Views
3K
  • Last Post
Replies
24
Views
9K
  • Last Post
Replies
2
Views
1K
  • Last Post
Replies
1
Views
1K
Replies
4
Views
2K
Replies
2
Views
832
Top