# Circular Motion

1. Dec 15, 2013

### haha1234

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

2. Relevant equations

3. The attempt at a solution
I have found the solution to part(B)
But I don't understand why the centripetal force is equal to the weight of the vehicle when the speed of the vehicle is maximum.

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Last edited: Dec 15, 2013
2. Dec 15, 2013

### xophergrunge

Do you mean maximum? The minimum speed would be zero.

3. Dec 15, 2013

### haha1234

Yes.Sorry for my typo

4. Dec 15, 2013

### xophergrunge

Okay. So, what would happen if the centripetal force became greater than the weight?

5. Dec 15, 2013

### Staff: Mentor

What are the only forces acting on the vehicle?

6. Dec 15, 2013

### haha1234

I don't know

7. Dec 15, 2013

### haha1234

Centripetal force and tangential force?

8. Dec 15, 2013

### Staff: Mentor

No, I'm talking about real forces. ("Centripetal force" is just the name given to whatever force is producing the centripetal acceleration. It's not a kind of force.)

Hint: One of those forces is gravity. What's the other? (I'm only interesting in forces that act at the top of the motion.)

9. Dec 15, 2013

### haha1234

Normal force? But I don't know how they are relevant to the maximum speed

10. Dec 15, 2013

### Staff: Mentor

Yes!

They are relevant because those two forces combine to give you the centripetal force.

What direction do those forces act? Express the centripetal force in terms of those forces.

The force of gravity cannot change, but what about the normal force?

11. Dec 15, 2013

### haha1234

Am I correct?
But when the centripetal force is greater than the weight, the normal force will be smaller than zero.
Is it correct?

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12. Dec 15, 2013

### Staff: Mentor

Yes.

Of course the normal force cannot be less than zero. What will happen is that the vehicle will leave the track if the speed is too great. The point where it is going as fast as it can and still maintain contact will be when the normal force goes to zero.

13. Dec 15, 2013

### haha1234

Why the vehicle will leave the track when the normal force becomes zero?
Sorry for my stupidity.:shy:

14. Dec 15, 2013

### Staff: Mentor

As long as the vehicle is pressing against the track there will be a normal force. When the normal force goes to zero, that means it is no longer pressing against the track--if it goes any faster, it begins to go flying off.