Redo Physics Exam Qs: Find Acceleration & Direction

[charitysmama]

Our professor is letting us redo the questions we missed on our exam for half-credit because the averages for his classes were 50, 60, and 70. I have a couple of q's I am needing help with, please.

What is the acceleration of a 1.8 kg physics book sliding down a 36 degree incline if the coefficient of kinetic friction, uk = 0.452?

What I have so far is Fnetx = Fg sin x (theta) - Ffk. But since Ffk is = uk x Fn, how do I find Fn? Would it be equal to Fg x cos (theta)?

Am I headed in the right direction at all?

 

[Shooting Star]

What I have so far is Fnetx = Fg sin x (theta) - Ffk. But since Ffk is = uk x Fn, how do I find Fn? Would it be equal to Fg x cos (theta)?

Am I headed in the right direction at all?

Right. You are almost there.

 

[charitysmama]

Okay... so I got Fnetx = 3.92 N. would Fnety = 0? How would I find acceleration from that? Completely lost after this. Thanks much.

 

[Shooting Star]

I don't know how you could be, after writing down the correct eqn...

If total F is along the plane downward, then
F = component of gravity along plane - frictional force
= mgsin(theta) - uk*mgcos(theta).

 

[charitysmama]

That is how i got the 3.92 N. So that is all?

 

[Shooting Star]

That is how i got the 3.92 N. So that is all?

Why, would you have liked it to be very difficult?

The mass will cancel out, so write the eqn in symbols like I have done. That'll make it even easier and neater.

Cheers.

 

[charitysmama]

I just knew there had to be something else to finding the acceleration is all. Thanks much for the help.