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## Homework Statement

Theres a pic.

## Homework Equations

##W_{friction}=W_{fr}=Δ(ME)##

##U_{spring}=U_s=\frac 1 2kx^2##

## The Attempt at a Solution

I found (a) using ##W_{fr}=Δ(ME)## which ##v=7,4 \frac m s##

For (b) I wrote;##\frac 1 2kx^2-\frac 1 2mv^2=W_{fr}##

##\frac 1 2kx^2-\frac 1 2mv^2=-F_{fr}x## (here x are the same and represents the comprassion distance)

so we get quadratic equation.

I found ##\frac 1 2mv^2=48988J##

so ##75000x^2+4400x-48988=0##

I solved it but didnt came the answer where did I go wrong ?

Thanks