Question

A 0. 16 kg hockey puck initially at rest on the ice requires a 0.157 N of horizontal force to set it in motion. Once the hockey puck is in motion, only a 0.047 N horizontal force is needed to keep it moving at a constant velocity.

a. Find the coefficient of static friction, Ms, between the puck and the ice.

Answer 1

Approximately
`0.10`, assuming that
`g = 9.81\; {\rm N\cdot kg^(-1)}` and a level surface.

Step-by-step explanation:

Under the assumption, the normal force between the ice and the hockey puck is equal to the weight of the puck:

`\begin{aligned}m\, g &= (0.16\; {\rm kg})\, (9.81\; {\rm N\cdot kg^(-1)}) \\ &\approx 1.57\; {\rm N}\end{aligned}`.

The friction on the puck is considered "static" when as long as the puck is not moving relative to that surface. In this question, the maximum value of this static friction is
`0.157\; {\rm N}`. When the external horizontal force exceeds
`0.157\; {\rm N}\!`, the puck would start moving relative to the ice.

Divide maximum static friction by the normal force to find the coefficient of static friction:

`\begin{aligned}\mu_(s) &= \frac{(\text{maximum static friction})}{(\text{normal force})} \\ &\approx \frac{0.157\; {\rm N}}{1.57\; {\rm N}} \\ &\approx 0.10\end{aligned}`.