Achild on a spinning playground ride is 0.36 m from the center of the ride. the centripetal force on the child is 19 n. what is the mass of the child if the child has a tangential speed of 0.54 m/s?

Centripetal force is easily calculated as long as you know the mass, m, of the object; its distance, r, from the center; and the tangential velocity, v. This equation is based on the metric system; note that the centripetal force, f, is measured in Newtons. 

F = mv^2 / r

19 N = m ( 0.54^2) / ( 0.36)

Solve for m

M = 23.5 kg

3. dark matter

empty space could also be a simple vacuum