Can someone please help me solve number seven

An observer that stands still as the electron moves by him, will observe

When the force acting on an object points at least partially in the direction of the motion the work done is considered to be negative

A0.580-kg rock is tied to the end of a string and is swung in a circle with a radius of 0.500 meters. the velocity of the rock is 4.50 m/s. what is the centripetal force acting on the rock? 15.5 n 5.22 n 69.8 n 23.5 n