Physics: Principles with Applications (7th Edition)

Use equation 7–2 applied to a single force, and re-arrange it to solve for the change in velocity. $$\Delta v = \frac{F \Delta t}{m}$$ Assume the skier moves to the right, then the friction force is directed to the left, and the velocity will decrease. $$\Delta v = \frac{(-25 N) (15 s)}{65 kg} = -5.8 m/s$$