this question can be spilt into two parts
- calculate the time taken by the ball released from the height to meet with the second ball
- using the the time calculated ,calculate the velocity of second ball
So how did i come to this conclusion
simple we are given that the balls meet at a point 40 m above ground ,so in this duration the released ball has covered (100-40)m right .SO BASICALLY U ARE GIVEN THAT THE TIME TAKEN BY THE RELEASED BALL TO COVER 60M FROM TOP OF BUILDING IS EQUAL TO TIME TAKEN BY SECOND BALL TO REACH 40 M FROM GROUND.
so now we calculate time taken by released ball to cover 60m
using
S=u*t+(a*t2)/2
here u=0
as initial it has no velocity
a= – gm/s2= – 10 m/s2
S= – 60m
(note in this sum i am taken scalars or vectors towards ground as -ve and away from ground as +ve)
(2S/a)1/2=t
t=(120/10)1/2sec
t=(12)1/2
now using data calculate the second ball velocity
let the initial velocity be V
t=(12)½ sec
a= – g=
S=40m
S=V*t+(a*t2)/2
by substuting the values we get
V=50/(3)1/2 m/sec