# Work and conservation of energy

1. Dec 11, 2004

### jbot2222

okay i applied work and conservation of energy to this problem, but the solution doenst come out right!

Suppose the roller coaster in the figure below passes point A with a speed of 1.76 m/s

If the average force of friction is equal to one fifth of its weight, with what speed will it reach point B? The distance traveled is 45.8 m and h = 29.4 m.

1/2mvi^2 + mgh - 1/5md = 1/2mvf^2

the m's cancel out and u should be able to solve for Vf, but it doest come out right!

2. Dec 11, 2004

### Pyrrhus

First your equation is wrong, because it says the force of friction is $\frac{1}{5}$ of its weight, so $F_{f} = \frac{1}{5}mg$ and the work done by friction $W_{f} = - \frac{1}{5}mgd$