physics
posted by Cassy on .
During a lift off , the thrust a rocket produces must overcome the force of gravity in order to lift the rocket off the ground. If a rocket with a mass of 5kg produces a force of 180N, how fast will the rocket be travelling 3 seconds after ignition?

First calculate the acceleration.
a = (ThrustWeight)/M = (180M*g)/M
180/5 g = 26.2 m/s^2
Assume the mass remains the same (although it actually must decrease as propellant is released) and use
Y = (1/2) a t^2
to compute how far it rises (Y) in t=3 seconds. 
I just noticed they asked for the velocity after three seconds, not the distance.
Use V = a t for velocity. 
thank you drwls