Question

A rocket has a mass of 100 kg. 90% of this is fuel. It ejects fuel vapours at the rate of 1 kg/sec with a velocity of 500 m/sec relative to the rocket. It is supposed that the rocket is outside the gravitational field. The initial upthrust on the rocket when it just starts moving upwards is

• A. Zero
• B. 500 N
• C. 1000 N
• D. 2000 N

Answer 1

Answer: (B)

500 N

Answer 2

Up thrust force $F = u \left( \frac { d m } { d t } \right)$