Well, first of all, the truck's velocity is constantly changing, not 'uniform'.
Velocity consists of speed and direction. So, even if the truck's speed is
constant, its direction keeps changing as long as it's on a circular curve,
so its velocity is constantly changing.
The force needed to keep a mass moving in a circle is
F = (mass) x (speed)² / (radius)
3300 N = (1600 kg) (13 m/s)² / R
3300 kg-m/s² = (1600 kg) (169 m²/s²) / R
R = (1600 kg) · (169 m²/s²) / (3300 kg·m/s²)
= (1600 · 169 / 3300) meters
= 81.9 meters
