# Energy Question Please Help

1. Aug 7, 2012

### Kennedy111

Energy Question!! Please Help!!

1. The problem statement, all variables and given/known data
A 170g hockey puck sliding at 25 m/s slows to a speed of 10 m/s in a distance of 7.5m. Determine the force of friction causing the puck to slow down.

m=170g
= 0.170kg
V1 = 25 m/s
V2= 10 m/s
d = 7.5 m/s

2. Relevant equations
Kinetic Energy = (1/2)(m)(v^2)
Work = Fd

3. The attempt at a solution

I'm really confused...

Kinetic Energy 1 = (1/2)(0.170kg)(25m/s)
= 2.125 J
Kinetic Energy 2 = (1/2)(0.170kg)(10m/s)
= 0.85 J

Kinetic Energy 2 - Kinetic Energy 1
0.85 J - 2.125 J = -1.325 J

Work = Fd
F = Work/d
= -1.325/7.5m
= -0.176666... which is wrong!

Please help!!

2. Aug 7, 2012

### azizlwl

Re: Energy Question!! Please Help!!

Check you equation.
v2

3. Aug 7, 2012

### Kennedy111

Re: Energy Question!! Please Help!!

Oh duh! That was dumb of me! Thank you so much!

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