# Rollercoaster normal force question

1. Feb 17, 2015

### leejos16

1. The problem statement, all variables and given/known data
In an amusement park ride called The Roundup, passengers stand inside a 19.0m -diameter rotating ring. After the ring has acquired sufficient speed, it tilts into a vertical plane, as shown in the figure

1. Suppose the ring rotates once every 5.50s . If a rider's mass is 52.0kg , with how much force does the ring push on her at the top of the ride?

2. What is the longest rotation period of the wheel that will prevent the riders from falling off at the top?

2. Relevant equations

3. The attempt at a solution
I'm pretty sure that I have to use the equation n=m(v^2)/r - mg to get the force, but I keep getting the wrong answer HelP~

Last edited: Feb 17, 2015
2. Feb 17, 2015

### BvU

Well hello Leejos, welcome to PF

The way things work here is you can get top notch assistance -- provided you make an effort yourself too, and show it.

$F_c = {m\;v^2\over r}$ is a good start and you can list it under 2. relevant equations. You have m, you have r but you need another equation to get a grip on v. What could that be ? And then you can calculate an $F_c$, but how does that relate to the force the ring exercises on the person ?

3. Feb 17, 2015

### Suraj M

Try relating time period to centrifugal force, without using v
Using $\omega$,, any idea?

4. Feb 17, 2015

### leejos16

OK first I did 5.50rps*2*pi*9.5 to get velocity. Than I used it in the equation n=52kg(328m/s)^2/9.5 - (52*9.8)
Is something wrong?

5. Feb 17, 2015

### BvU

No YES! 5.5 s/turn is not the same as 5.5 turns per second !

6. Feb 17, 2015

### BvU

Except I hadn't seen that equation before in this thread. But it's the right one.

7. Feb 17, 2015

### BvU

But that's because I didn't read carefully enough
I am now so brainwashed that I look for relevant equations under relevant equations.
And for attempt at solution I look under attempt at solution

8. Feb 17, 2015

### leejos16

hmm then are you saying that my velocity is wrong then? Any suggesstions how to solve it then?

9. Feb 17, 2015

### BvU

See post #5.

10. Feb 17, 2015

### Suraj M

Leejos, if your have so much trouble finding v.
try $find \omega$ from the given time $$\omega = \frac{2 \pi}{T}$$
then use
$$F_c = MR\omega²$$

Last edited: Feb 17, 2015