A rocket is fired straight up from the ground with an initial velocity of 900 feet per second.
(a) How long does it take the rocket to reach 4200 feet?
(b) When will the rocket hit the ground?
You need to use newton's third law of motion...
max height height rocket ascends
acceleration due to gravity (32.1522 ft/s it is negative as it is accting downward)
initial vel(900 ft/s)
final vel(0 m/s at top pos it doesnt have velocity)
Where time in the air.
This is, in my opinion, a really bad problem. The equation Anonymous1 gives, as well as will work for something thrown upward so that the only force is that of gravity. But the whole point of a rocket is that it continues firing as it goes up so that is NOT true.