# Free Body Diagram of a incline

1. Jan 23, 2014

### thonwer

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

Draw a free body diagram of the incline. Build the free body diagram of the man. Which is the force which makes the man to go up the incline?

http://imagizer.imageshack.us/v2/800x600q90/46/t92m.png [Broken]

2. Relevant equations

Newton's 2º Law

3. The attempt at a solution

For the incline I've put a reaction from the floor, a reaction from the van, weight from the man and the box and the normal reaction from the incline to the weights of the man and the box.

For the man I've put, the weight, the normal reaction from the incline to the weight, and the friction force going to the top of the incline.

I suspect I am missing some force for the incline free body diagram, can you help me please?

Last edited by a moderator: May 6, 2017
2. Jan 23, 2014

### .Scott

Is there force between the man and the box?

3. Jan 23, 2014

### thonwer

Yes, do I have to draw it too?

4. Jan 23, 2014

### .Scott

It's asking for the free body diagram of the man.
(So, yes)

5. Jan 23, 2014

### thonwer

My question is about the free body diagram of the incline not the man.

6. Jan 23, 2014

### .Scott

In the case of the incline, you could treat the man and the box as a unit.
If it was my homework assignment, I would treat them separately. It wouldn't make a difference until the box started to move or the man started to slip. At that point, you would have a mixture of inertial and kinetic friction.

7. Jan 23, 2014

### tiny-tim

hi thonwer!
no, you're not applying the basic rule of a free body diagram:

only include the forces on the body

the weight of the box (or the man) only acts on the box (or the man), it does not act on the incline, and so it does not go on the free body diagram

the reaction from the box (or the man) does act on the incline, and so it does go on the free body diagram

(also you've missed out the friction, though it would be easier if you simply said "reaction" (not "normal reaction"), since that includes the friction)

8. Jan 23, 2014

### thonwer

Ok, so I have the floor and the van forces, but I don't really understand how do the block and the man affect the incline, I know there is a friction force but I don't know its direction in the incline but I know it for the man

9. Jan 23, 2014

### tiny-tim

between the man and the incline:​

there's a normal force, just like the normal force when the man is ion the ground

and there's a friction force

you can combine both of them into the total reaction force

between the incline and the man:​

exactly the same forces, equal in magnitude but in the opposite direction