(adsbygoogle = window.adsbygoogle || []).push({}); It's another block/incline question -- plus friction and a force

This shouldn't be difficult. I've tinkered for a few hours, and I know I'm just missing some ticky thing about getting it setup right. I'm going to post the /whole/ question here, but really if somebody can just help me get started, I should be able to solve it.

In fact, I've already made an incorrect attempt...so the computer has given me new numbers. I'm truly more interested in learning the concept than getting the right answer...

1. The problem statement, all variables and given/known data

Block M = 7.50 kg is initially moving up the incline and is increasing speed with a = .585 m/s^2.

The applied force F is horizontal.

The coefficients of friction between the block and incline are μs = 0.443 and μk = 0.312. The angle of the incline is 25.0 degrees.

Find:

(a) What is the magnitude of the force F?

(b) What is the normal force N between the block and incline?

(c) What is the magnitude of the force of friction on the block?

2. Relevant equations

I know n should be mgcos(theta)

I know F=ma

and that the resistant force from the friction (And we'll use the kinetic friction, I believe) is friction*normal

3. The attempt at a solution

I tried to start with finding "N" -- but I believe N is affected by the force being applied. I've tried breaking down the mass into x andy components, as well as the force, and the force from friction -- but since I'm not getting my normal force right, I'm not getting the resistant force from friction right, and that throws the whole thing off.

Where I'm getting super lost is this:

If the surface was frictionless, I could easily determine the force from the acceleration. Because friction is involved I need "N" -- but I can't figure out how to find "N" without "F" -- so lost as to how to find "F" from "a" without "N" to help me know what the friction-force is.

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# Homework Help: It's another block/incline question - plus friction and a force

**Physics Forums | Science Articles, Homework Help, Discussion**