Two particles are thrown vertically upwards along the same line

with the same initial velocity u = 30 m/s, but at different times.

The second particle is thrown t seconds after the first. What should

be the minimum value of t so that the particles collide in mid-air?

Neglect air resistance. Express your answer in MKS or SI system

of units.

time should b less than the first particle come on ground applying neton second eqn                                                               s=ut+1/2at2                                                                                                                                                                          0=30t-1/2*10*t2                                                                                                                                                         30=5t=>t=6s