EK Physics 313 (Static Equilibrium)

[IlyaR]

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Hi, I had some trouble with this problem initially, and after looking over the answer I'm even more confused. The answer mentions that upwards forces must equal downward, thus Tcos30= mg + f, however from my understanding, since the sign would be moving downwards, wouldn't f (frictional force) be upwards?

The entire answer seems convoluted, I was hoping for a simpler explanation.

Thanks very much!

 

[Romz]

This took me FOREVER to figure out.

Seriously, searched SDN for the same question, saw that they figured the question was flawed and moved on.

It's a **** question and unlikely to come up on the MCAT. (Well, I hope )

Why is it friction going down? Because we're assuming that the plank is rotating clockwise! We know that friction is opposite the direction of motion, so if we are moving clockwise, Fk points down along gravity!

Also, they're wrong in saying Kinetic friction. Should be static as the damn thing isn't even moving.

 

[IlyaR]

Ah right, the Fs going down makes sense actually. Definitely hope this type of question won't be on the exam, hah