1. Dec 6, 2012

### infinitylord

I had gotten an answer that I'm very unsure of so I would like clarification and corrections if necessary. Thank you
1.) A block is sliding along a horizontal frictionless surface at 10.3 m/s. It then slides up an incline that has friction and is tilted at 18.0 degrees. Then it slides onto another horizontal frictionless surface that is 1.50 m above the lower one traveling at 9.13 m/s. What is the coefficient of friction on the ramp?

2.) Superman need to stop Lex Luther who is driving a 1.2x10^4 kg car at 150 km/hr. If he stops the car in 2.3s, how much power did Superman use to stop the car?

3. The attempt at a solution
1.)
KEi - ƩW = PEgf + KEf
1/2mv^2 - μmgcosθ = mghf + 1/2mv^2
μ = (ghf - 1/2vi^2 + 1/2vf^2)/-gcosθ(hf-hi)
that was the formula I finished with(even though it can be simplified)
I'm just wondering if this is right at all

2.)
P= W/Δt
W= Fd
F= m(vi/Δt)/Δt
d= VavΔt=1/2VfΔt
W= (m(vi/Δt)/Δt)1/2vfΔt
P= ((m(vi/Δt)1/2vfΔt)/Δt
That was my final formula for that. Again, I can simplify it but this would still give the "correct" answer.