P = (50Kg)(2x10^4 m/s)
P = 1,000,000Kgm/s
Due to the law of conservation of momentum & since thrust is constant (until out of fuel), the downwards momentum is counteracted by an upwards momentum that launches the rocket.
1,000,000Kgm/s = (5x10^4)v
v = 20m/s
One second later, the...