A 905 kg test car travels around a 3.25 km circular track. If the magnitude of the centripetal force is 2140 N, what is the car's speed?

Consider that a centripetal force can be written as:

Fc = m v2 r

where r is the radius.

so in your case: circular distance=2πr

3.25 * 103 = 2⋅3.14⋅r

remember to change into meters.

r = 3.25 * 103 6.28 = 517m

2,140 = 905 * v^2 * 517

v = √ 1.1 * 106 905 = 34.9 m/s ≈ 35 m/s = 126 km / hr