# Circular Motion, weights and gravitation

1. Oct 9, 2004

### dsandhu

Hello I am having alot of difficulty figuring out these last four problems for my homework. if anyone can help me I would greatly appreciate it. My teacher is refusing to help me for some reason. THanks!

1.planet Jupiter is about 320 times as massive as the Earth. Thus, it has been claimed that a person would be crushed by the force of gravity on Jupiter since people can't survive more than a few g's. Use the following astronomical data for Jupiter: mass = 1.9 *10^27 kg, equatorial radius = 7.1 *10^4 km, rotation period 9 hr 55 min. Take the centripetal acceleration into account. Calculate the number of g's a person would experience if she could stand on the equator of Jupiter.

2. A train traveling at a constant speed rounds a curve of radius 325 m. A chandelier suspended from the ceiling swings out to an angle of 20.0° throughout the turn. What is the speed of the train?

3. Lastly , At what minimum speed must a roller coaster be traveling when upside down at the top of a circle if the passengers are not to fall out? Assume a radius of curvature of 9.8 m.

4. Estimate the force a person must exert on a string attached to a 0.170 kg ball to make the ball revolve in a horizontal circle of radious 0.600 m. The ball makes 1.20 revolutions per second. Do not ignore the weight of the ball. In particular, find the magnitude of FT, and the angle it makes with the horizontal. [Hint: Set the horizontal component of FT equal to ma(R); also, since there is no vertical motion, what can you say about the vertical component of FT?]

I would greatly appreciate anyone's help even the slightest.
Thanks

2. Oct 9, 2004

### Staff: Mentor

Show your work and where you got stuck. You'll get plenty of help. (Read the sticky at the top of the forum.)

Also: Do not post the same question in multiple forums! You also posted this one here: https://www.physicsforums.com/showthread.php?t=46838 [Broken], which I have moved to College Help (where it belongs).

Last edited by a moderator: May 1, 2017
3. Oct 9, 2004

### dsandhu

For Question 1, I am using the equation g = GM/r^2 , where G is 6.67 *10^-11, M is 1.9 *10^27 kg, and r is 7.1 *10^4 km, and I get 2.514 * 10^7. But then the question asks what is the number of g's in Earth. I don't understand what that last part means.

For Question 2, I thought about using the equation a = v^2/r, but they don't give us acceleration of the train, and wouldn't we need that to find the y component of the acceleration. I honestly have no idea where to go from there.

For Question 3, I am using the same equation a = v^2/r, they give us the radius of the system but not the acceleration.

For Question 4, I honestly have no idea where to start or where to end.

Any help would be greatly appreciated.
Thank You

4. Oct 9, 2004

### nolachrymose

For number three, here's a possible hint: acceleration due to gravity is a known constant.

5. Oct 9, 2004

### dsandhu

Thank You, Thank You Thank You So much, I really appreciate it, I guess I wasn't understanding the problem. I really Appreciate it!!

6. Oct 9, 2004

### arildno

1. But you know that the "g" on earth, satisfies:
$$g_{e}=\frac{GM_{e}}{R^{2}_{e}}$$
where the "e" subscript is Earth quantities..