Hatrack River Forum: another physics question...

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Posted by kelly smith (Member # 5075) on :

i'm not thinking too clearly right now cuz im not seeing the answer to this question, if someone knows how to do it you'll be my hero for life.

"you slide a .50 kg cart from rest across the floor with a push that takes .70 seconds to get up to a 4.0 m/s speed. The net force is 2.86 Newtons. What is the frictional force on the cart during the slide?

-i'm pretty sure the formula I have to use is
Force= push-friction but i dont know the push force for some reason.
any physics people in the room?

Posted by saxon75 (Member # 4589) on :

The force of the push can be determined by utilizing F=ma.

It's sort of a trick question.

Posted by kelly smith (Member # 5075) on :

i used f=ma to find the force that i gave in the problem (2.86) now i want to use that to find the frictional force...

Posted by fugu13 (Member # 2859) on :

I don't believe there's enough information.

Rephrasing the problem, I can take a box on any surface, and by simply applying more force for the surfaces with the higher frictional coefficient achieve exactly that acceleration. We can know the net force based on that, but the frictional force will always be proportional to both the normal force (which we know) and the coefficient of kinetic friction (which we don't).

Posted by Bokonon (Member # 480) on :

fugu is right, unless you have the coefficient of friction in your notes...

Wait, fugu, can't you split up F(total) into F(friction) + F(momentum)? Maybe then it is possible? Or at least describe the equation.

-Bok

Posted by Hobbes (Member # 433) on :

Can you give us the exact phrasing of the orginal question?

Hobbes [Smile]

Posted by fugu13 (Member # 2859) on :

You can split it up, but that leaves two unknowns: F(friction) and F(exerted). The only one we know is F(total, aka net).

Posted by kelly smith (Member # 5075) on :

thanks for your help guys, i'll try it!

Posted by fugu13 (Member # 2859) on :

You won't be able to solve it unless you have other information.

Posted by Bokonon (Member # 480) on :

Well, you could say that the floor is frictionless... If it were a trick question.

-Bok