Projected upwards with a speed of 25ms-1 at t=0 from the ground. Show with a velocity time graph that there are 2 times when the object passes through a point 30m above and show that the interval between the two times is 1 second. If the time passing through those two points is t_1 and t_2 then show that the time is \frac{t_1 t_2}{2} when the projectile is at its maximum height.