A constant friction force of 25N acts on a 65-kg skier for 20s. What is the skier’s change in velocity?

Question

A constant friction force of 25N acts on a 65-kg skier for 20s. What is the skier’s change in velocity?

Answer 1

the key point here is that forces cause change in motion that we call acceleration. This relationship is given by Newton's second law:

F = ma

assuming there are no other forces acting on the skier, we can compute the acceleration of the skier due to this force:

a = F/m = 25 N/65 kg = 0.38 m/s/s

meaning the speed of the skier slows down by 0.38 m/s for each second of motion.  In 20 s of motion, the speed will change by 20x0.38 or 7.6 m/s