A pendulum of mass 1.0 kg is suspended from the roof of a car travelling on a level road. An observer in the car notices that the pendulum string makes an angle of 10 deg with the vertical. What is the acceleration of the car?
The Attempt at a Solution
I drew the FBD diagram (attached) and I wrote the vertical and horizontal force equations:
Vertically: Tcos 10 deg=mg
So I got he equation mgtan10deg=mv^2/r after putting the equations together. But I don't know the radius of the pendulum, so I don't know how to solve the problem.