Posted by beavis on .
(ignore the other question i posted this is the right one)
A rocket has a preignition mass of 1100kg. On ignition it burns fuel at rate of 20kg s1 producing a thrust of 10000N. How long after ignition of the fuel, will the rocket lift off?
also explain how is it possible for a rocket to accelerate in space.
(i cant work it outt. i know it involves the rocket thrust equation some how, the newtons 2nd law and suvat's..) thank you

physics 
drwls,
The rocket weight is
M = (1100  20 t)*g = 10,780  196*t newtons
That equals the thrust when
196*t = 780 N
t = 3.98 seconds
Rockets acclerate during each stage because the thrust stays the same while the mass decreases (until burnout, when the fuel of that stage is gone). 
physics 
beavis,
ahh thank you so much!
can you write the actual formulas that you've used because im not sure if i understood it correctly