12th grade PYSICS
posted by Samii .
A 45.7kg boy on a swing moves in a circular arc of radius 3.80 m.At the lowest position, the child's speed reaches 2.78 m/s. Determine the magnitude of the tension in each of the two vertical support chains.
i used mv^2/r, but i keep getting the answer wrong. the answer is suppose to be 270 m/s
please help

A motiom of an objects along the circumference of a circle.

A rock tied to a string is swung around in a circle with a radius of 10 ft. The centripetal acceleration is 16.9 ft/sec2. Calculate the speed of the rock.