How you do this? Help plz (1 Viewer)

[TigerMaster]

Calculate the acceleration of a 5x10^4 kg rocket just after lift-off, if it's motor is expelling 50 Kg of exhaust at 2x10^4 m/s every second.

 

[ThreeSciences]

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 rocket weighs 50Kg less.

1,000,000Kgm/s = (5x10^4 - 50)v
v = 20.02 (2 d.p)

Acceleration = (change in velocity) / (time)
= (20.02 - 20) / 1
= 0.02m/s/s