The time difference between their landing is 2.04 seconds.
The ball thrown vertical upwards will take double of the time taken by the ball thrown vertically downwards.
Time difference, = 2t - t = t
t = √(2h/g)
where;
Apply the principle of conservation of energy;
¹/₂mv² = mgh
h = v²/2g
where;
h = (20²)/(2 x 9.8)
h = 20.41 m
t = √(2 x 20.41 / 9.8)
t = 2.04 s
Thus, the time difference between their landing is 2.04 seconds.
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