A particle is projected from the ground at t = 0 so that on its way it just clears two vertical walls of equal height on the ground. If the particle passes just grazing the top of the walls at time t=t1 and t=t2 then calculate the height of the walls.
Time of Flight = t1+t2
Assume initial velocity = u
Angle of projection = θ
Now we know time of flight = 2vsin θg=t1+t2
⇒usin θ=(t1+t2)g2 .............(i)
Applying equation of motion in y-axis for part of motion where it reaches wall 1
uy=usin θ
sy=h
t=t1
a=−g
⇒h=usin θt1−12gt21 ........(ii)
Putting equation (i) in (ii) we get
h=(t1+t2)g2t1−12gt21
⇒h=g2t1[t1+t2−t1]
h=12gt1t2