# Carnival uniform motion

1. Sep 28, 2007

### splac6996

1. The problem statement, all variables and given/known data
You've taken your neighbor's young child to the carnival to ride the rides. She wants to ride The Rocket. Eight rocket-shaped cars hang by chains from the outside edge of a large steel disk. A vertical axle through the center of the ride turns the disk, causing the cars to revolve in a circle. You've just finished taking physics, so you decide to figure out the speed of the cars while you wait. You estimate that the disk is 5 m in diameter and the chains are 6 m long. The ride takes 10 s to reach full speed, then the cars swing out until the chains are 20 from vertical.

2. Relevant equations

3. The attempt at a solution

2. Sep 28, 2007

### Chi Meson

You've been told a few times already...

c'mon!

3. Sep 28, 2007

### splac6996

I am not sure what is going on

4. Sep 28, 2007

### Chi Meson

Forget the neighbor's kid. Picture a ball on a string going around an upright pole.

Draw that picture.

Make a free-body-diagram of the forces on the ball.

5. Sep 28, 2007

### splac6996

Fx=Nsin(theta)=ma=m*v^2/r
Fy=Ncos(theta)-mg=o

6. Sep 28, 2007

### Chi Meson

OK, now you need to use the information to find the tangential speed. Rotational kinematics.

7. Sep 28, 2007

### splac6996

Using that information I get a speed of 8.93m/s which is not correct.

v=sqrt(rgtan(theta)

am I missing some idea

Last edited: Sep 28, 2007
8. Sep 29, 2007

### rootX

it's 4.033?

9. Sep 29, 2007

### Chi Meson

I misread the problem. The radius has to be re-evaluated. Rather than a string attached to a pole, is is a string attached to a 2.5 m radius disk. The radius of the circle taken by the chair will be 2.5 m + the horizontal component of the chain's length.

10. Sep 30, 2007

### splac6996

thanks

11. Nov 14, 2007

### Need_Help!!!

I have done

v=$$\sqrt{8.5*9.80*tan(20)}$$
= 13.65

computer told me that it is not correct.

where did I went wrong?

Do I have to consider the "time factor" of 10 seconds as described in this problem?

12. Oct 22, 2008

### humanities

the radius isn't 8.5, it's 2.5 plus the "horizontal component of the chain's length", which is 6sin(20).