Spring Force, Distance Problem

1. Nov 27, 2012

rocapp

1. The problem statement, all variables and given/known data
The spring in the figure has a spring constant of 1400N/m . It is compressed 16.0cm , then launches a 200g block. The horizontal surface is frictionless, but the block's coefficient of kinetic friction on the incline is 0.210.

FIGURE ATTACHED

What distance d does the block sail through the air?

2. Relevant equations

F(spring)=-kx
F(friction)=μf*FN
Work=Fdcos(θ)
Work=(0.5mv22)-(0.5mv12)

3. The attempt at a solution

F(spring)=(-1400 N/m)(0.16 m)= 224 N

F(friction)=(0.210)(cos(45))(0.2)(9.8)= 0.29 N

224-0.29= 223.71

Work=223.71d
Work=(0.5)(0.2)(?)-(0.5)(0.2)(?)

I think that I should be finding the work and then find distance by dividing by the force. However, I'm not sure how to find the two velocities.

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2. Nov 27, 2012

tiny-tim

hi rocapp!
you can't find d from work or energy, you'll need the usual projectile equations

to find the initial speed (just before d), use the work-energy method that you have been using (with the block starting with zero speed), but use gravity also