Work (Conservation of Energy/Newton's Laws)

1. The problem statement, all variables and given/known data
MP 11.44

Sam, whose mass is 75kg, straps on his skis and starts down a 50-m-high, 20degree frictionless slope. A strong headwind exerts a horizontal force of 200N on him as he skies. Find Sam's speed at the bottom (a) using work and evergy (b) Using Newton's laws

2. Relevant equations

Dot product

3. The attempt at a solution

(a)

vf=sqrt(2*(mgh+F*(h/sin20)*cos(160))/m)

Which got me= 15.7270m/s

(b)

a=(mgsin(20)-200/cos(20))/m

Which got me: 12.225m/s

I'm not sure where I went wrong. Any thoughts?
 PhysOrg.com science news on PhysOrg.com >> City-life changes blackbird personalities, study shows>> Origins of 'The Hoff' crab revealed (w/ Video)>> Older males make better fathers: Mature male beetles work harder, care less about female infidelity

Mentor
Blog Entries: 1
 Quote by jzwiep Fnet = Fg - Fheadwind a=(mgsin(20)-200/cos(20))/m
What's the component of the 200N force parallel to the slope?
 200/cos(20) means that component of force along the slope is greater than the force itself! You should write 200*cos20. Well, maybe it is just a typing error (like evergy) because you wrote mg*sin20 and not mg/sin20

Work (Conservation of Energy/Newton's Laws)

Thanks. I drew the triangle backwards.

 Similar discussions for: Work (Conservation of Energy/Newton's Laws) Thread Forum Replies Introductory Physics Homework 2 General Physics 15 General Physics 13 General Physics 2