Coupla things wrong with this question, Sam.
Let's clean those up first, and then we'll work on the answer.
-- The car is NOT moving with uniform velocity.
'Velocity' includes both speed and direction. If either of these
changes, it's a change of velocity.
On a circular track, the car's direction is CONSTANTLY changing,
so its velocity is too.
The thing that's uniform is its speed, not its velocity.
-- A 'neutron' is a subatomic particle found in the nucleus of most
atoms. It's not a unit of force. The unit of force is the 'Newton'.
_______________________
OK. A centripetal force of 6,000 newtons keeps 1,200 kg of mass
moving in a circle at 20 m/s.
The formula:
Centripetal force = (mass) (speed)² / (radius)
Multiply each side
by 'radius': (centripetal force) x (radius) = (mass) x (speed)²
Divide each side by
'centripetal force': Radius = (mass) x (speed)² / (centripetal force)
Write in the numbers
that we know: Radius = (1200 kg) (20 m/s)² / (6000 Newtons)
= (1200 kg) (400 m²/s²) / (6000 Newtons)
= (480,000 kg-m²/s²) / (6000 kg-m/s²)
= (480,000 / 6000) meters
= 80 meters .