What Is the Minimum Force to Keep a Sled From Slipping on an Inclined Plane?

AI Thread Summary
To prevent a sled weighing 70 N from slipping down a 20° inclined plane, the minimum force parallel to the plane must be calculated using the coefficients of static and kinetic friction. A user expresses confusion over their calculations and seeks help, particularly regarding the direction of the friction force. It is clarified that when the sled is on the verge of slipping, the friction force acts up the slope, contrary to the user's initial assumption of it acting downwards. Properly identifying the direction of friction is crucial for solving the problem accurately. Understanding these dynamics is essential for determining the minimum force required to maintain the sled's position on the incline.
Stianos
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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?
 
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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.
 
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.
 
Stianos said:
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.
 

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