Rockets and Orbits: Practice Problem Solutions

1. Hot gas is thrown out of the nozzle downward; the gas pushes back on the rocket with an equal and opposite force, which is thrust.

2. It carries its own fuel and oxidizer and pushes against its exhaust, not against air or ground. Without air to slow it, it works even better.

3. Δv = 3 x ln 5 = 3 x 1.61 = about 4.8 km/s.

4. Reaching orbit needs about 9.4 km/s; with a single stage and chemical fuel that needs about 96% of the rocket's mass to be fuel, leaving almost nothing for tanks, engines and payload.

5. Dropping each stage when its fuel is used up so that the rocket no longer has to carry the empty tanks and engines. That makes reaching orbit practical.

6. He launched the first liquid-fueled rocket, in Auburn, Massachusetts.

7. About 7.8 km/s (28,000 km/h).