# Newton's Second Law Problems

Stianos
1. A loaded penguin sled weighing 70 N rests on a plane inclined at 20° to the horizontal. Between the sled and the plane the coefficient of static friction is 0.25, and the coefficient of kinetic friction is 0.16.
(a) What is the minimum magnitude of the force F, parallel to the plane, that will prevent the sled from slipping down the plane?

3. I cannot figure out what I'm doing wrong. I draw my free body diagram, write out an x/y chart, and then solve.
I write a lot, so I'm just post an imgur link with my work in it.
http://imgur.com/pCNNQ

Can anyone show me what I'm doing wrong?

Homework Helper
Gold Member
Hello, Stianos.

If the sled is on the verge of slipping down the slope, what is the direction of the friction force?

Also, looks like you're treating the coefficient of friction as being the same as the force of friction.

Stianos
If the sled is on the verge of slipping down the slope, then the friction is pointing up the slope?
Should I not do that? What should I do instead?
Thank you for responding, sorry I couldn't not respond immediately.

Homework Helper
Gold Member
If the sled is on the verge of slipping down the slope, then the friction is pointing up the slope?
Yes. It looked to me that you had the friction pointing down the slope.