I need help with Physics!!!?

Question

A hockey puck is hit on a frozen lake and starts moving with a speed of 21 m/s. Exactly 5.00 s later, its speed is 5.3 m/s. What is the average value of the coefficient of kinetic friction between puck and ice? how far does the puck travel during this 5.00 s interval?

Answer 1

The problem can be solved by considering the energy lost to friction
Kinetic .5*m*v^2
versus friction
m*g*µ*d

the kinetic diff is
.5*m*(21^2-5.3^2)

or m*206.455

The distance traveled is
t*(v1+v2)/2
5*(21+5.3)/2
d=65.75 m

so
m*g*µ*65.75=m*206.455
µ=206.455/(g*65.75)
µ=0.320

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