## College Physics (4th Edition)

The work done by friction is $-552.5~J$
The total work done by gravity $W_g$ and friction $W_f$ on the skateboarder is equal to the skateboarder's change in kinetic energy. We can find the work done by friction: $W_g+W_f = \frac{1}{2}mv^2$ $W_f = \frac{1}{2}mv^2 - W_g$ $W_f = \frac{1}{2}mv^2 - mgh$ $W_f = \frac{1}{2}(65.0~kg)(9.00~m/s)^2 - (65.0~kg)(9.80~m/s^2)(5.00~m)$ $W_f = -552.5~J$ The work done by friction is $-552.5~J$