# Check my answers to these questions

1. Nov 15, 2008

### phys1618

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

1.in order to cause a moving body to pursue a cirular path, it is necessary to apply
a. gravitation force
b. centripetal force

2. a body traveling in a circle at constant speed
a. not accelerated
b. has a constant velocity
d. has an outward radial acceleration

3.centripetal force needed to keep the earth in orbit is provided by
a. its roation on its axis
b. gravitational pull of the sun
c. gravitational pull of the moon

2. Relevant equations

3. The attempt at a solution
1. b
2. b
3. b

2. Nov 16, 2008

### alphysicist

Hi phys1618,

One of your answers is incorrect. Since we are not supposed to simply give out answers on this forum, can you provide a reason why you chose those answers?

3. Nov 16, 2008

### phys1618

for 1. b.centripetal force because in order for things to move in a circular path it needs the centripetal force or else it will just fall down, which is gravitational force. it is center seeking

2. b this one i wasnt too sure about ..I chose b velocity is constant because of uniform
circular motion. the object speed's remain constant..

3. This was the one which gave me a lot of thinking..but i chose b. gravitational of the sun because the earth revolves around the sun...so the force from the sun...keeps the earth moving.

4. Nov 16, 2008

### alphysicist

This one is the one that was wrong. The speed is constant, but the velocity is the speed and the direction of motion. Since it is moving in a circle, it's direction of motion is always changing, so the velocity is always changing.

5. Nov 16, 2008

### phys1618

you are so Right!! that's true, my teacher had mentioned that to us so many times....i cant believe i forgot! thank you for reminding me!! cuz it is ann impt concept.

so that means the answer is a..not accelerated
correct???

again, thank you....I appreciates all your help!

6. Nov 16, 2008

### alphysicist

If there is no acceleration, that means the velocity is not changing, so that cannot be right.

7. Nov 16, 2008

### phz

Look at Newton's second law: F = ma. Is there a force acting on the circulating body?

8. Nov 16, 2008

### phys1618

it would be an outward force....so outward acceleration?

9. Nov 16, 2008

### alphysicist

What force is outward?

10. Nov 16, 2008

### phys1618

i was thinking about spinning a string with a ball in a circular motion....so i thought it was the force from the hand to the ball that makes it in motion.....i guess i was wrong...

unless its inward acceleration due to centripetal force, which is through gravity???

Sorry for my lack of knowledge...please be patient and thanks

11. Nov 16, 2008

### borgwal

For question 1 you had the correct answer: b. In order to answer question 2 correctly, answer this: is the centripetal acceleration inward or outward?

12. Nov 16, 2008

### phz

Centripetal force doesn't have to be from gravity, it is just the case eg between the earth and the sun. You have answered this in 1).

The image of a circulating ball in a string is a good one. Think of the ball - what force acts on the ball? Which direction has this force? Think of F = ma.

13. Nov 16, 2008

### phys1618

centripetal force is inward.. so therefore answer to number 2 is c.inward radial acceleration..correct???

Gosh, i hope this is right this time. =x...thank you all!!!

14. Nov 17, 2008

### borgwal

Yep!

15. Nov 17, 2008

### phys1618

thank you to all of you!!!