# Object on an incline with friction

1. Sep 13, 2010

### jinx007

An object of mass 3 kg lies on a rough plane inclined at 45 degree to the horizontal. The coefficient of friction is 0.2 and a force of 10 N acts at 30 degree to the object. Calculate the friction. According to the booklet the answer is 3.24 N

My work

F = u R

Normal reaction = 10 sin 30 + 30 cos 45 = 26.2

U = 0.2 x 26.2 = 5.24 N

I am confused HELPPPPPP.. where is the fault, is there something that i have not considered

2. Sep 13, 2010

### w3390

Re: Mechanics

What is the 30 degrees measured relative to? Is it relative to the plane the block is sitting on or relative to the horizontal?

3. Sep 13, 2010

### jinx007

Re: Mechanics

It is relative to the block(object)

4. Sep 13, 2010

### w3390

Re: Mechanics

So you have a block sitting on a slope. Is the block moving?

5. Sep 13, 2010

### JonF

Re: Mechanics

Your normal reaction has a sign error. Also that cos 45 should be sin 45. I know numerically they are the same thing, but for what it actually represents, it should be sin.

I'll give you a hint, think about what the normal force is conceptually, not mathematically

Last edited: Sep 13, 2010