A particle is projected horizontally from the top of a tower with velocity 20 m/s. Then the time after which its speed will be 202  m/s . (Take g = 10 m/s2)

After time t, horizontal component of velocity of the particle is, VH = 20 m/s and its vertical component of  velocity isVv =0 +  gt=10t  m/s.∴     VH2+Vv2= 2022⇒   202 +  10t2=800  ⇒  t=2  sec.