# Help for physics static and kinetic friction

#### sundeepsingh

help for physics static and kinetic friction.
Question:
A 70 Newtons Penguin is on a 50 N. sled. the static friction between the penguin and sled is 0.671 and the kinetic friction between the sled and the SNOW is 0.119. FInd the maximum horizontal force that can be applied without the penguin sliding off the sled?

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#### Doc Al

Mentor

Hint: What is the maximum value of the static friction that the sled can exert on the penguin? What acceleration is associated with that force? Apply Newton's 2nd law to find the applied force on the sled.

#### sundeepsingh

this is what i did.
the friction force between sled and snow is= FN X u=(70.1+50)*0.119=14.2919 N.
the friction force between the penguin and sled = (70.1)*0.671=47.0371, therefore, the max horizontal force that can be applied to the sled without causing the penguin to slide off the sled=14.2919+47.0371=61.329 N. But this is wrong, where m i wrong plz tell me.

#### Pengwuino

Gold Member
Did someone say penguin :D

#### Doc Al

Mentor
sundeepsingh said:
the friction force between sled and snow is= FN X u=(70.1+50)*0.119=14.2919 N.
OK. (But the penguin weighs 70N, not 70.1N.)
the friction force between the penguin and sled = (70.1)*0.671=47.0371,
OK. (Same comment.)
therefore, the max horizontal force that can be applied to the sled without causing the penguin to slide off the sled=14.2919+47.0371=61.329 N.
Nope. First find the maximum acceleration of the penguin. (What force acts on the penguin?) Then figure out what force must be applied to the sled so that the sled+penguin has that acceleration. (Don't forget to consider the friction force between sled and snow that must be overcome.)

#### sundeepsingh

THANKS a lot DOC AL, i LUV U lol :P

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