Question

A stone is dropped from the top of a tower 50 m high. simultaneously another stone is thrown upwards with a speed of 20m/s. calculate the time at which both the stone across each other

Answer 1

Let the stone cross after t seconds at height h from ground
For stone 1
height travelled = 50-h
time taken = t seconds
u = 0
s=ut + 1/2at^2
(50-h)=1/2gt^2 (1)

for second stone
height travelled =h
u=20
h=20t-1/2gt^2 (2) (g is opposing the motion)
solve the 2 equations to get h and t. t is the answer
adding the equations
50=20t
t=2.5 seconds