# Homework Help: Energy and Friction in a block

1. May 5, 2017

### HaoPhysics

1. The problem statement, all variables and given/known data

2. Relevant equations
The block has potential energy U at the top of the ramp, and this is transfered to kinetic energy K at the bottom, which is then trasnfered to work done by friction, Wfr.
U = K Conservation of energy
K = Wfr Conservation of energy
g = 10 m/s2

3. The attempt at a solution
U = mgh = 3*45*10 = 1350 J
1350 J = Wfr = Ffr * d = m*g*u*d = 3*10*1*d
1350 = 30*d
d = 45 m

This does not match the answers. Am I doing anything wrong?

2. May 5, 2017

### Staff: Mentor

Your calculations are correct. There is likely an error in the problem statement. I suspect that they intended the coefficient of kinetic friction to be 0.1. Your answer of 45 m is correct for the given information.

3. May 5, 2017

### HaoPhysics

That is a very good point. We usually don't see coefficients of friction to be 1.0, so it probably was 0.1. I just wanted to make sure my understanding of work-energy relationship was correct. Thanks!