Question

A 2000 kg rocket in free space expels 0.5 kg of gas per second at exhaust velocity 400 ms^–1 for 5 seconds. What is the increase in speed of rocket in this time –

• A. 2000 ms^–1
• B. 200 ms^–1
• C. 0.5 ms^–1
• D. Zero

Answer 1

Answer: (C)

0.5 ms^–1

Answer 2

$\frac { \mathrm { dm } } { \mathrm { dt } }$ × u = M

0.5 × 400 = 2000 × ̃ Dv = 0.5 ms^–1