# Homework Help: Magnitude and direction of the force of the seat on you?

1. Dec 14, 2008

### charan1

1. The problem statement, all variables and given/known data
One fine spring day you decide to skip class and go to the amusement park to ride the loopthe-
loop roller coaster. At the bottom of the loop, you’re moving with a speed of 20 m/s in a vertical circle 20 m
in diameter. What’s the magnitude and direction of the force of the seat on you? Assume your mass is 50 kg.

2. Relevant equations

3. The attempt at a solution

20m/s=omega x 10m

=5,000 N

I drew the FBD and the only forces are the Normal which I assume is the seats force on the rider which I further moved towards thinking that would be the Force towards the center thus the equation
Fr=mass x omega2 x radius, and the other force is (of course) g.

-Charan

Last edited: Dec 14, 2008
2. Dec 14, 2008

### Mthees08

Re: Loop-the-loop

F(centripetal)=V^2/R because you are moving in a circle there is a centripetal force, always. At the bottom it is opposite of weight and the normal you feel is w-Fc at the top it is creating a normal if I remember correctly. so It is Fc+W=N

3. Dec 15, 2008

### charan1

Re: Loop-the-loop

Oh I see thank you I also just found it in my book

at the bottom N=mg+mv2/r
and at the top N=mv2/r - mg

so in this case it is asking for the Normal force at the bottom and that is the first equation.

so:

N=(50kg)(g) + (50kg)(20m/s)2/10m
N=2,490N

4. Dec 15, 2008

### NBAJam100

Re: Loop-the-loop

Charan,

Just so you know how to get that equation and not memorize it, here are some steps you might take to help you understand why that is the case.

First draw a free-body and analyze the forces acting on you due to the seat. After drawing the diagram you will see that you have a Fn going up and a Fw going down. So if you use newtons second law you get.

Efy=ma(c)

Fn-Fw=m(V^2/r) -----> Fn=Fw+m(V^2/r)

It will probably stick better if you understand why those equations are true

5. Dec 15, 2008

### PhanthomJay

Re: Loop-the-loop

That's all very well, but please don't blindly find formulas in the book and try to apply them without understanding them.

6. Dec 16, 2008