# Mistake in solving for work in physics?

1. Homework Statement
a student wearing a frictionless in-line skates on a horizontal surface is pushed by a friend with a constant force of 45N. How far must the student be pushed, starting from rest, so that her final kinetic energy is 352J?

2. Homework Equations

3. The Attempt at a Solution
KE=1/2MV^2
352=1/2*(45/9.81)*V^2
Vf=12.39 and Vi=0 since it starts from rest

Wnet=1/2MVf^2-1/2MVi^2
1/2*(45/9.81)*12.39^2=352.31

Wnet=FnetDCosX
352.31=45dcos0
d=7.83m

I just wanted to know if that was a correct way of solving it or did i make a mistake somewhere?
thx for the help.

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Doc Al
Mentor
3. The Attempt at a Solution
KE=1/2MV^2
352=1/2*(45/9.81)*V^2
Vf=12.39 and Vi=0 since it starts from rest

Wnet=1/2MVf^2-1/2MVi^2
1/2*(45/9.81)*12.39^2=352.31
Since you are given the final KE, these calculations are not needed. (Note how error creeps in: 352.31 should really be 352.)

Wnet=FnetDCosX
352.31=45dcos0
d=7.83m
This is all you need. (Use the given value for KE.)

the Wnet is always the same as KE?

Doc Al
Mentor
the Wnet is always the same as KE?
The net work will equal the change in KE. That's the so-called Work-KE theorem.

ooo thxx hehe