Question

(b) A ball is thrown vertically upwards with

velocity of 20 m/s from the top of a tower of
height 25 m from ground. How long does it
remain in air? (g = 10 m/s²)

Answer 1

5 seconds

Step-by-step explanation:

The vertical position of the ball will be given by the equation

df = do + vo t + 1/2 a t^2 df = final position = 0 ( on the ground

do = original position ( 25 m )

vo = original velocity (+ 20 m/s)

a = - 10 m/s^2

So this becomes

0 = 25 + 20 t - 1/2 (10)t^2

= - 5 t^2 +20 t + 25 Use Quadratic Formula a = -5 b=20 c = 25

to find the positive value of t = 5 seconds