How to find Friction Force and Coefficient of Friction?

  • #1

Homework Statement



A horizontal force of 200 n is required to cause a 15 kg block to slide up a 20degree incline with acceleration of 25 cm/s^2. Find the friction force on the block and the coefficient of friction.
ANSWERS:
Friction force = 134N
Coefficient of Friction = 0.65

Homework Equations


Ff = u Fn

The Attempt at a Solution


I can't figure out where to begin.
I'm not sure if it's relevant, but I found:
Fg to be 147.15 N
horizontal component to be 50.33 N
Vertical component to be 138.28N
 

Answers and Replies

  • #2
anyone there?

Part one:
Fgcos(20) - Ff = ma
138.28N - Ff = 15 x .25m/s^2
138.28N - Ff = 3.75
-138.28 -138.28
-Ff=-134.53
Ff=134.53N
(Hopefully this is correct?)

Part 2:
Ff = u Fn
u = Ff / Fn
u = 134.53N / 138.28N
u = .97

But the answer should be .65.
What am I doing wrong? The normal force should be 138.28 because 147.15cos(20) is 138.28, right?
Ugh, this is too confusing. Please help!
 

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