A body is projected horizontally from the top of a tower with velocity 20 m/s. Then the time after which the magntiude of its velocity becomes 40 m/s.

After time ‘t’, horizontal component of its velocity is 20 m/s and vertical component of velocity is V where V = 0 + gt = 10 t m/s.∴ 202+10t2=402⇒t=23sec