What is the speed of the roller coaster at the bottom of the dip?

[Amber430]

A roller coaster at an amusement park has a dip that bottoms out in a vertical circle of radius r. A passenger feels the seat of the car pushing upward on her with a force equal to three times her weight as she goes through the dip. If r = 22.0 m, how fast is the roller coaster traveling at the bottom of the dip?

At the bottom of the dip, Fn -mg= m(v^2/r). I plugged in 3m for Fn since it's 3 times her weight, and I'm not sure if I'm doing this right.

 

[Doc Al]

At the bottom of the dip, Fn -mg= m(v^2/r).

Good.

I plugged in 3m for Fn since it's 3 times her weight, and I'm not sure if I'm doing this right.

Careful. 3m is a mass, not a force. What's her weight? What's 3 times her weight?

 

[w3390]

It looks like everything you have done is correct. When you say that you plugged in 3m for Fn you mean (3m)*g, right? If so, it looks correct.

 

[Amber430]

No, I was not using 3mg, just 3m. That's where I messed it up. It makes sense now, thank you so much!