# Homework Help: Net Forces

1. Feb 14, 2009

### NickS606

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

A 2kg mass starts from rest and slides down an inclined plane 8.0X10m long in 0.50s. What net force is acting on the mass along the incline?

2. Relevant equations

3. The attempt at a solution

I don't even know where to begin.

2. Feb 14, 2009

### Delphi51

This is an accelerated motion problem. Use a motion formula to find the acceleration.

3. Feb 14, 2009

### Dr.D

Try drawing a free body diagram and then sum the forces on the body.

4. Feb 15, 2009

### NickS606

I'm sorry I am still new, can I get a better explanation please?

5. Feb 15, 2009

### Hootenanny

Staff Emeritus
Can you work out the acceleration of the object?

6. Feb 15, 2009

### NickS606

How can I do that?

7. Feb 15, 2009

### Hootenanny

Staff Emeritus
Do you know any Kinematic (SUVAT) equations?

8. Feb 15, 2009

### NickS606

I'm just gonna go ahead and say I have never even heard of those equations.

9. Feb 15, 2009

### Hootenanny

Staff Emeritus
Really? Then I'm going to go ahead and say take a look in your textbook or class notes and find them.

Alternatively, you can find them https://www.physicsforums.com/showpost.php?p=905663&postcount=2". However, I must say that I will be extremely surprised if your teacher hasn't mention them, but set you a homework that requires them.

Last edited by a moderator: Apr 24, 2017
10. Feb 15, 2009

### NickS606

Ya I don't really recall those. Anyways, would I do $$a_{ave} = \Delta v / \Delta t$$

I did 12N/3.5s and my answer is 3.4, is this correct?

11. Feb 15, 2009

### Hootenanny

Staff Emeritus
Perhaps, but we'll have to do some work first.
No. Did you just pluck those numbers out of thin air?

Returning to the question, what do the dimensions 8x10m refer to? Height and width or height and hypotenuse or width and hypotenuse? Do you have a diagram?

12. Feb 15, 2009

### NickS606

I got the numbers out of the question, and there is no diagram, it is height and width for sure though.

13. Feb 15, 2009

### Hootenanny

Staff Emeritus
Okay. Have you looked for the kinematic equations in your notes or text?

14. Feb 15, 2009

### NickS606

Well there aren't many notes and all I could find was this equation $$v_{ave} = \Delta x / \Delta t$$

The teacher isn't really that great and won't help much, that's why I am here.

15. Feb 15, 2009

### Hootenanny

Staff Emeritus
Okay, well we cannot use that equation. Try reading http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/1DKin/U1L6a.html" [Broken] and see if it jogs your memory.

Last edited by a moderator: May 4, 2017
16. Feb 15, 2009

### NickS606

I'm just not getting it, I assume the equation to be used is

d=vi*t+1.5*a*t^2

17. Feb 15, 2009

### Hootenanny

Staff Emeritus
The highlighted coefficient should be 0.5 rather than 1.5, but yes, this is the equation to use. Can you start filling in the known variables?

18. Feb 15, 2009

### Delphi51

Yes, that formula will do it if the initial velocity is zero.

19. Feb 15, 2009

### NickS606

Is it d=0*.50s+.5*a*.50s^2

I put a for acceleration because I don't know what acceleration is :/

20. Feb 15, 2009

### Hootenanny

Staff Emeritus
One may use the above formula even if the initial velocity is non-zero.
Acceleration is what you want to find out! You need to solve for the acceleration.

Now, what about the distance traveled?