2 particles are projected vertically up one after another from the same point at same initial speed u. T is the time interval between the 2 projections, where T<2u/g. Find what further time elapses before the particles collide, and find their speeds immediately before impact. The particles will collide when they are at equal height. Ive started by finding the distance formula for particle 1 but am unsure how i should use T in an equation for particle 2??