Well, first of all, a car moving around a circular curve is not moving
with uniform velocity. The direction of motion is part of velocity, and
the direction is constantly changing on a curve.
The centripetal force that keeps an object moving in a circle is
     Force = (mass of the object) · (speed)² / (radius of the circle)
     F = m s² / r
We want to know the radius, to rearrange the formula to give us
the radius as a function of everything else.
                      F   = m s² / r
Multiply each side by 'r':    F· r = m · s²
Divide each side by 'F':       r = m · s² / F  Â
We know all the numbers on the right side,
so we can pluggum in:
           r =     m    ·    s²   /   F
            r = (1200 kg) · (20 m/s)² / (6000 N) .
I'm pretty sure you can finish it up from here.
                   Â
