The height of a rocket above t seconds after firing is given by s=ut-5t^2, where u represents the initial speed of the rocket. If the initial speed is 70 ms^-1, find the amount of time the rocket is in the air and the time the rocket is above 30m.

Which statement best describes the superposition principle? a.) if two in-phase waves arrive simultaneously at a point, their amplitudes add up b.) if two out-of-phase waves arrive simultaneously at a point, their amplitudes add up c.) if two in-phase waves arrive at a point one after another, their amplitudes add up d.) if two out-of-phase waves arrive at a point one after another, their amplitudes adds up