# Small block on a track - Finding Normal forces and

1. Nov 2, 2011

### nukeman

Small block on a track - Finding Normal forces and....

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

Here is the question. Can someone please help, since I missed the section of class that went over this, any my textbook does not cover this well. Look below at question 1, a) and b)

2. Relevant equations

3. The attempt at a solution

2. Nov 2, 2011

### grzz

Re: Small block on a track - Finding Normal forces and....

Which are the forces at point Q?

3. Nov 2, 2011

### nukeman

Re: Small block on a track - Finding Normal forces and....

At point Q - Forces are Gravity down... Does it have tangential and radial?

4. Nov 2, 2011

### grzz

Re: Small block on a track - Finding Normal forces and....

The block is touching the track. Hence besides the weight there is also the ...

5. Nov 2, 2011

### nukeman

Re: Small block on a track - Finding Normal forces and....

Force of gravity and the normal force

6. Nov 2, 2011

### grzz

Re: Small block on a track - Finding Normal forces and....

Correct.
Now for a mass to perform circular motion, it needs a ...

7. Nov 2, 2011

### nukeman

Re: Small block on a track - Finding Normal forces and....

Force?

8. Nov 2, 2011

### grzz

Re: Small block on a track - Finding Normal forces and....

What do we call this particular force?

9. Nov 2, 2011

### nukeman

Re: Small block on a track - Finding Normal forces and....

I am not sure. Momentum force?

10. Nov 2, 2011

### grzz

Re: Small block on a track - Finding Normal forces and....

Any mass performing circular motion needs a force towards the centre of the circle. This particular force is called ...

11. Nov 2, 2011

### nukeman

Re: Small block on a track - Finding Normal forces and....

Centripetal Force?

12. Nov 2, 2011

### grzz

Re: Small block on a track - Finding Normal forces and....

CORRECT.

what is the formula for this centripetal force in terms of the speed at Q?

13. Nov 2, 2011

### nukeman

Re: Small block on a track - Finding Normal forces and....

I am not sure on that... I cant find it in my book (awfull book). :(

?

14. Nov 2, 2011

### grzz

Re: Small block on a track - Finding Normal forces and....

This forum is for helping and not for doing the work for you.
Try looking up 'centripeta force' on internet search engine. That is the way to learn.

15. Nov 2, 2011

### nukeman

Re: Small block on a track - Finding Normal forces and....

Did not mean to imply that.

F = MAc = MV^2/r

Is that it? what is the c ?

16. Nov 2, 2011

### grzz

Re: Small block on a track - Finding Normal forces and....

It is ok. You are welcome to this forum!

You got the right formula.
A - acceleration, c- centripetal.

Now try to find the speed at point Q.

17. Nov 2, 2011

### nukeman

Re: Small block on a track - Finding Normal forces and....

This is where i have trouble.

When i plug everything in:

F = (.100)(2.00)^2 / (.150)

I get 2.66 ?

18. Nov 2, 2011

### grzz

Re: Small block on a track - Finding Normal forces and....

Remember that we were talking about the mass when it is at point Q. So we are trying to find the centripetal force at point Q. But the speed you are using is 2m/s which is the speed at a higher point and not the speed at Q.

Try to find the speed at Q.

19. Nov 2, 2011

### nukeman

Re: Small block on a track - Finding Normal forces and....

I dont understand how I would change that formula to find the centripetal force at point Q

20. Nov 2, 2011

### grzz

Re: Small block on a track - Finding Normal forces and....

The first part of the problem was to find the normal force at Q.

To do this we need to find the centripetal force at Q.

This centripetal force = mv$^{2}$/R.
Hence we need the speed v, at Q.
Try using the conservation of energy principle to find the speed at Q.