Answer : The actual velocity of the ping-pong ball is, 5 m/s
Explanation :
Using Pythagorean theorem :

The diagram is shown below.
From the diagram we conclude that,
AB = 4 m/s
BC = 3 m/s
AC = ?

Now put all the given values in this formula, we get


Therefore, the actual velocity of the ping-pong ball is, 5 m/s