Please help me with physics?

Question

A hockey puck is hit on a frozen lake and starts moving with a speed of 13.30 m/s. Exactly 5.3 s later, its speed is 6.30 m/s. 

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

Answer 1

The Initial Speed of the hockey puck is 13.30 m/sec.

The Speed of the hockey puck after 5.3 sec is 6.30 m/sec.

Therefore

Acceleration of the hockey puck  = Change in velocity / time.

Acceleration of the hockey puck = (6.30 - 13.30) / 5.3

Acceleration of the hockey puck = -1.5 m/sec².

Force on the hockey puck is equal to the Frictional Force but both are in opposite direction.

Force on the hockey puck = -Frictional Force ( ' - ' indicates the direction)

Force on the hockey puck = ma.

Frictional Force = µ * Normal Force

Normal force = mg

Frictional Force = µ * mg

Now

Force on the hockey puck = - Frictional Force

ma = - (µ * mg)

a = - (µ * g)

µ = - (a / g)

µ = -(-1.5) / 9.8

µ = 0.15

Therefore the coefficient of Frictional Force is 0.15.