A 45 kg boy sits on a horse on a carousel 5.0 m from the center of the circle. he makes a revolution every 8.0 s. calculate his speed.
what is centripetal force acting on the boy?

For every complete revolution the boy makes around the center of the carousel, he travels a distance of 2π (5.0 m) = 10π m, which gives a linear speed of

v = (10π m) / (8.0 s) ≈ 3.927 m/s

Then his centripetal acceleration would be

a = v ² / (5.0 m) ≈ 3.084 m/s²

so that the centripetal force exerted on him has magnitude

F = (45 kg) a ≈ 138.791 N ≈ 140 N

(rounded to 2 significant digits)