1. The problem statement, all variables and given/known data A pullback toy car is pulled back. How far will it go before it stops? x(0)=0 v(0)=0 a(x<x0)=-k(x0-x) a(x>x0)=μg v(tf)=0 tf=D 2. Relevant equations Fs=-kx F=mg Ff=μF 3. The attempt at a solution d2x/dt2=1/m(k(x0-x)-μmg) Later in the run spring constant is irrelevant, so d2/dt2=1/m(-μmg) I think I can figure out the μ by pulling the car back on the ramp and lowering the angle between the ramp and the surface until car starts rolling. Then the tangent of that angle tanθ=μ Would this be correct? Also, what experiment or method would you propose to figure out the coefficient of spring? Disassembling the toy is not an option. I apologize I didn't put formulas the proper way, however I couldn't get Latex to work even though I followed FAQ instructions.