A ball is thrown vertically upwards with velocity ‘u’. the speed with which it falls to the world again is:

Hint: The speed of an object is the rate of change of its position with reference to a frame of reference, and may be a function of your time . Velocity is like a specification of an object's speed and direction of motion.

Complete step by step solution:
For vertically upward motion: g is negative because it opposes the motion.
v = u – gt
0 = u – gt
t = u/g …..(1)
For vertically downward motion: g is positive because it is within the direction of motion.
v = u + gt
v = 0 + gt
t = v/g …..(2)
 From equation 1 and a couple of
v = u
When one throws a ball upwards with velocity 'u' its velocity decreases thanks to downward gravitational pull. it'll reach some extent where its velocity becomes zero.
Let the time taken by the ball to subside from a height be 't'.
Using,v=u+gt.
For example, when a ball is thrown up within the air, the ball's velocity is initially upward. Since gravity pulls the thing toward the world with a continuing acceleration g, the magnitude of velocity decreases because the ball approaches maximum height. At the very best point in its trajectory, the ball has zero velocity, and therefore the magnitude of velocity increases again because the ball falls back toward the ground.

Note:
PE= MGh, which shows that P.E. is directly proportional to height, hence as height increases, P.E. increases. Once we throw a ball upwards, its speed retards gradually. This is often because the world produces gravity which brings down everything that goes up. So when a ball is thrown upward the gravity applies force to bring it down which decreases its speed of rising.