Sam, whose mass is 75 kg, straps on his skis and starts down a 50-m-high, 20 degree frictionless slope. A strong headwind exerts a horizontal force of 200 N on him as he skies.
Find his speed at the bottom of the slope using Newton's Law
Find his speed at the bottom of the slope using Energy
Conservation of Energy
F = ma
vf^2 = vi^2 + 2ad
ME_i = ME_f
The Attempt at a Solution
I set up a drawing, found the length of the slope, did the force analysis, and got the following (Newton's Laws part):
Length of the slope = 146.19m
Force down the slope = m*g*sin(20) = 251.3848N
Force of wind up the slope = 200/cos(20) = 212.835
So Fnet = 251.3848-212.835= 38.549
a = Fnet/m = 38.549/75 = .5139
vf*vf = vi*vi + 2(a)(d)
vf*vf = 0 + 2(.5139)(146.19)
vf = sqrt(150.28) = 12.25 m/s
Not sure where I went wrong.
As for the energy part, I'm not sure how to approach it.