Question

A ball is thrown vertically upwards with a speed of 10m/s from the top of a tower 400m high. Find the time taken by ball to reach the ground.

Answer 1

Answer: 10s

Explanation: First find the distance and time taken to reach where the velocity of the ball becomes zero at max.ht.

(A) u=10m/s

v=0, g=10 so using v=u+at

t= 10/10= 1s this is the time taken to reach max. Ht. which is H=½gt²

H=½×10×1²= 5m

(B) Now second part is when ball falls from this max ht = 5+400=405m

u=0, using H=½gt²

405=½×10×t²

t²=81

Thus, t=9s

Now total time taken=upward+downward journey

T=1+9=10

Ans. 10s.