How can I solve this automobile physics problem involving a helium balloon?

[Hellsing834]

Hey guys, I needed help with this question:

An automobile traveling at 90 km/hr rounds a long sweeping curve of radius 250m. The air conditioner is on and the windows are rolled up so that the air within the car moves essentially as a rigid body. A child in the back seat is holding onto the string of a helium-filled balloon. On a straight road the string is vertical, but in the curve its not. Determine the magnitude and direction of the string angle as measured from the vertical.

I have no ideas on how to start, I know i have to use angular velocity/free body digrams, but the thing is, this is the only info that is given, nothing else. Could you please give some hints on how I can start this problem?

This is what I have done so far, although I can't really go ahead because the mass is unknown :(

[PLAIN]http://img806.imageshack.us/img806/8880/photobd.jpg

Thank you!

 

[WolfeSieben]

I actually had a similar problem in my first year mechanics course.
I can't recall the intimate details, but you have to figure out the minimum angle that the road has to be banked so that the car can take it at 90 km/h if the road was frictionless.
That will be the angle the balloon will be at if the air in the car is considered a rigid body.

 

[Drakkith]

Well, let's start with seeing if you have everything you need to solve this. Take the data given and plug it into your formulas you have.

What do you have and what do you think you need?

Edit: Which mass do you think you need?