# Homework Help: Potential Energy and WET (Incline with friction)

1. Oct 17, 2008

### closer

A 6.00 kg block is set into motion up an inclined plane with an initial speed of v0 = 8.50 m/s (Fig. P7.23). The block comes to rest after traveling 3.00 m along the plane, which is inclined at an angle of 30.0° to the horizontal.

(a) Determine the friction force exerted on the block (assumed to be constant).
(b) What is the coefficient of kinetic friction?

Wfk + Wg = -.5mvi2
(fk)(x) + (m)(g)(h) = (-.5)(m)(vi2)
(fk)(3) + (6)(9.8)(3sin30) = (-.5)(6)(8.5^2)
fk = -101.65

Final answer is incorrect. Cannot move on to (b) without understanding (a). Any ideas?

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2. Oct 17, 2008

### LowlyPion

Looks to me like the wrong sign.

KE = PE + Wf

3. Oct 17, 2008

### closer

Tried positive 101.65; the answer is still incorrect.

4. Oct 17, 2008

### LowlyPion

When you change the sign there you don't get the same answer. That was my point.

5. Oct 17, 2008

### closer

The change in KE is negative though.

6. Oct 17, 2008

### LowlyPion

It's the conservation of Energy.

Where does the KE go?

It goes into PE and to work done by friction.

KE = PE + Wf