Homework Help: Incline plane - Did I do this right?

1. Dec 13, 2004

tony873004

This is just a question I made up because there'll probably be one like this on our final exam.

A 5 kg block is on an incline plane of 50 degrees. coeffecient of friction is 0.5. Will it slide?

N = mg cos(50)
N = 31.529
friction = mu * N
friction = 15.764

force down = ma

f =m g cos(50)
f = 31.529

force down > friction so it will slide.

2. Dec 13, 2004

Pyrrhus

Actually the force making it slide it's the x component of gravity $mg \sin \theta$

and yes if $mg \sin \theta > \mu mg \cos \theta$ then it will slide.

3. Dec 13, 2004

tony873004

Thank you...

4. Dec 13, 2004

Pyrrhus

Why don't you try finding the coefficient of friction that will avoid the system from sliding or finding the angle it will not slide an a specific coefficient of friction? Those are some of the common problems asked.

5. Dec 13, 2004

tony873004

if it slides when mg sin theta > mg cos theta, then when they equal that should be the minimum mu necessary to keep it from sliding.
mg sin theta = mu mg cos theta
mu = (mg sin theta) / (mg cos theta)

but this gives me an answer greater than 1.

6. Dec 13, 2004

Pyrrhus

Because the inequality says [itex] \tan \theta > \mu [/tex] that's why you are getting a greater value.

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