Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (4th Edition)

The thermal energy is equal in magnitude to the work done by friction. We can use the work-energy theorem to find the work done by friction. $KE_1+PE_1+W_f = KE_2+PE_2$ $0+mgh+W_f = \frac{1}{2}mv^2+0$ $W_f = \frac{1}{2}mv^2-mgh$ $W_f = \frac{1}{2}(30~kg)(11~m/s)^2-(30~kg)(9.80~m/s^2)(8.0~m)$ $W_f = -537~J$ The amount of thermal energy created by friction is 537 J.