Asked by KS

A girl is sledding down a slope that is inclined at 30º with respect to the horizontal. The wind is aiding the motion by providing a steady force of 131 N that is parallel to the motion of the sled. The combined mass of the girl and the sled is 59.9 kg, and the coefficient of kinetic friction between the snow and the runners of the sled is 0.217. How much time is required for the sled to travel down a 243-m slope, starting from rest?

I found the acceleration to be 134.06m/s^2. I plugged it into the x=vot+1/2at^2 to find the time, but it turns out to be incorrect. Is my acceleration not correct? Please help, thanks!
Answered by bobpursley
Your acceleration is exceedling wrong. That is 900 feet in a second, faster than a speeding bullet. Superman would be thrilled to have that acceleration, assuming his cape didn't tear off. Lois would never make it.

gravity down the slope: mg*sinTheta
wind force down the slope: 131sinTheta
wond force upwards normal to slope: 131CosTheta
friction force on slope (mg-windforcenormal)mu


net force down slope=ma
gravity+windforcedown-friction=ma
mgsinTheta+131SinTheta-(mg-131cosTheta)mu=ma

now solve for a. I am pretty certain is not close to my hero, superman.
Answered by KS
Okay, I solved for a and came out with a=4.28m/s^2 (thank you!). However, when I plugged it into the formula to solve for time, my answer is still incorrect. Am I using the wrong formula?
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