A small boy of mass 0.2kg moves uniformly in a circle on a horizontal frictionless surface, attached by a cord 0.2m long to a pin set in the surface. If the body makes two complete revolutions per second, find the force P exterted on it by the cord.
The speed of the boy is
V = 2* 2 pi R per second
Compute that and then compute the centripetal force
F = M V^2/R
M is the mass and R is the radius of the cord.