4. 1 kg ball on the end of a string is revolving in a vertical circle 2m in diameter under the influence of gravity only (see figure). The speed of the ball is 7.5 m/s when it is at the lowest point.

a. (10 points)

What is the tension in the string when the ball is at its lowest point?

b. (10 points)

What will be the speed of the ball when it is at the highest point of the circle?