Redo Physics Exam Qs: Find Acceleration & Direction

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Homework Help Overview

The discussion revolves around calculating the acceleration of a physics book sliding down an incline, considering the effects of kinetic friction. The problem involves understanding forces acting on the book, specifically gravitational and frictional forces, in the context of physics principles related to motion on inclined planes.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the net force acting on the book and the relationship between gravitational force components and friction. Questions arise regarding the calculation of the normal force and its relationship to gravitational force on an incline.

Discussion Status

Some participants have provided guidance on the equations involved, while others express uncertainty about subsequent steps in the calculation process. There is an ongoing exploration of the correct approach to finding acceleration, with various interpretations of the forces at play being discussed.

Contextual Notes

Participants are working under the constraints of a homework assignment, which may limit the information they can use or the methods they can apply. There is a focus on understanding the physics concepts rather than simply arriving at a numerical answer.

charitysmama
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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?
 
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charitysmama said:
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.
 
Okay... so I got Fnetx = 3.92 N. would Fnety = 0? How would I find acceleration from that? Completely lost after this. Thanks much.
 
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).
 
That is how i got the 3.92 N. So that is all?
 
charitysmama said:
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.
 
I just knew there had to be something else to finding the acceleration is all. Thanks much for the help.
 

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