# A hockey puck is hit on a frozen lake and starts moving with a speed of 12.0 m/s. Exactly 5.0 s later, its speed is 6.0 m/s. What is the puck’s average acceleration, and what is the coefficient of kinetic friction between puck and ice?

Aug 11, 2018

Average acceleration is $- {\text{1.2 ms}}^{-} 2$ and coefficient of frictional force is $0.12$

#### Explanation:

Average deceleration $\left({a}_{v}\right)$ is equal to change in velocity in given time.

So, a_v =((12-6) \ "ms"^(-1))/"5 s" = 6/5 \ "ms"^-2

Now, if this happened due to frictional force then we can say that the frictional force acting was

$f = \mu N = \mu m g$

where $\mu$ is coefficient of frictional force and $m$ is its mass.

So, the deceleration caused by the force is

$\frac{f}{m} = \mu g$

And this is equal to ${a}_{v}$. So,

${a}_{v} = \mu g$

Putting $g = 9.8 m {s}^{-} 2$, we get

mu=a/g=(6/5) \ "ms"^(-2)xx(1/(9.8 \ "ms"^(-2)))=0.12