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A 5000 kg rocket is set for vertical firing. The exhaust speed is 800 ms–1. To give an initial upward acceleration of 20 ms–2, the amount of gas ejected per second to supply the needed thrust will be (g = 10 ms–2)
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- 127.5 kg s–1
- 187.5 kg s–1
- 185.5 kg s–1
- 137.5 kg s–1
Correct Option: B
Given : Mass of rocket (m) = 5000 kg
Exhaust speed (v) = 800 m/s
Acceleration of rocket (a) = 20 m/s²
Gravitational acceleration (g) = 10 m/s²
We know that upward force
F = m (g + a) = 5000 (10 +20)
= 5000 × 30 = 150000 N.
We also know that amount of gas ejected
 |  | = | = | = 187.5 kg/s | ||||
| dt | v | 800 |
