a stone A is dropped from the top of tower and B is thrown downward from same point 2 seconds later with initial velocity of 30 ms , if the same stone A and B reach the ground at same time, find height of the tower

Answer 1

da = 0.5g*t^2 = 4.9*2^2=19.6 m. in 2 s.
Va = Vo + g*t = 0 + 9.8*2 = 19.6 m/s in
2 s.

Da = Db - 19.6
19.6t + 4.9t^2 = 30t + 4.9t^2 - 19.6
19.6t - 30t + 4.9t^2 - 4.9t^2 = -19.6
-10.4t = -19.6
t = 1.88 s. to reach gnd.

h = 30t + 4.9t^2 = 30*1.88 + 4.9*1.88^2
= 73.9 m.