Question

A rocket already in flight fires its second stage. This accelerates the rocket at a rate of 80 m/s/s to a velocity of 3600 m/s in 25 seconds. What was the rocket's velocity, v, just before the second stage was fired? ​

Answer 1

Assuming constant acceleration, we have

a (average) = a = ∆v/∆t

So if v is the rocket's velocity just before the second stage, we have

80 m/s² = (3600 m/s - v)/(25 s)

===>   v = 3600 m/s - (80 m/s²) (25 s) = 1600 m/s