# Homework Help: Sphere on an incline plane against a wall

1. Nov 18, 2012

### ethan340

1. The problem statement, all variables and given/known data
Find all of the forces acting on the sphere. The problem must be solved in variables. A sphere, mass m, is resting on an incline plane at θ relative to the horizontal. The sphere is also resting against a perpendicular wall relative to the horizontal. Gravity = g.

2. Relevant equations
f perp. to incline plane= mg(cos θ)
f parallel = mg(sin θ)
fnormal = g

3. The attempt at a solution
Setting up those equations was as far as i got; i still need the force of the sphere against the wall perpendicular to the ground i think

Last edited: Nov 18, 2012
2. Nov 18, 2012

### haruspex

The question ought to state that the surfaces are smooth, otherwise it's indeterminate.
Anyway, your equations are wrong: the first two because they omit any force from the wall; the third because it equates a force to an acceleration, and besides, fnormal is normal to what?
Before writing equations, list and name all the forces that are relevant, stating whatever is known about the directions in which they act and their lines of action. Then choose two directions in which to resolve and write the statics equations.

3. Nov 18, 2012

### ethan340

haruspex, i appreciate that you've taken the time to read my post and convey what you believe is helpful to me, but unfortunately, your post isn't all that helpful to me. you fail to understand the difference between incorrectness and incompleteness, and the fact that you don't know what i mean by normal force worries me that you aren't qualified to answer this question. by the way, the surface is smooth unless specified otherwise.

in any case, i would like advice on how to solve the problem correctly and understand the methodology behind it.

4. Nov 19, 2012

### haruspex

If an equation is missing a term it is incorrect.
I know what a normal force is, but it doesn't mean much unless you specify the plane it's normal to. In this case, you already have "f perp. to incline plane", so I guess it's not that. The only other surface of contact is the wall, but normal to the wall would be horizontal.
You have it equal to g (but you probably mean mg), so it sounds like a vertical force.