Question

A hockey puck is hit on a frozen lake and
starts moving with a speed of 12.1 m/s. Four
seconds later, its speed is 6.7 m/s.
What is its average acceleration? The ac-
celeration of gravity is 9.8 m/s2 .
Answer in units of m/s2.

What is the average value of the coefficient of
kinetic friction between puck and ice?

How far does the puck travel during this 4 s
interval?
Answer in units of m.

Answer 1

a = change in v /change in time
= (6.7 - 12.1)/4
= -1.35 m/s^2

F = m a = - mu m g
so
mu = 1.35/9.8 = .138

average speed = (12.1+6.7)/2 = 9.4
9.4*4 = 37.6 meters

Answer 2

Thank you! That makes much more sense!