The answer is 80 m.
Centripetal force (F) is a force that makes body move around a circular curve. The unit of force is N (N = kg * m/s²).
It can be represented as:

where:
m - mass
v - velocity
r - radius of the curve
We have:
m = 1,200 kg
V = 20 m/s
F = 6,000 N = 6,000 kg * m/s²
We need radius of the curve:
r = ?
So, if
, then:

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