Aball is tossed with enough speed straight up so that it is in the air several seconds. (a) what is the velocity of the ball when it reaches its highest point

The velocity of the ball at it's highest point is zero.

Explanation:

When we toss a ball upwards as we know that it's motion is an uniformly accelerated motion with acceleration = in the downward direction.

Hence as we throw the ball upwards it's speed will go on decreasing as it gains height. The ball will stop gaining height when it's velocity becomes zero and the ball starts to descend again towards earth.

If the ball is tossed at an angle with the horizontal in that case it's velocity at the top most point will not be zero but in our case since the ball is tossed vertically it's velocity at the topmost point will become zero.