A rocket moves forward in the vacuum of space because
Correct answer: B. the momentum carried away by the exhaust gases is balanced by an equal forward momentum of the rocket
- A. the exhaust gases push against the air behind it
- B. the momentum carried away by the exhaust gases is balanced by an equal forward momentum of the rocket
- C. gravity pulls it forward
- D. it becomes lighter as fuel burns
Explanation
Conservation of momentum, equivalently Newton's third law, means expelling mass backwards at speed drives the rocket forwards, and no surrounding medium is needed. This is why rockets work best in a vacuum, where there is no air resistance. Losing mass does help the acceleration but is not the source of the thrust.
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About Linear Momentum
Linear momentum is the vector product of mass and velocity, p = mv, and changes when a net external force acts. Work includes impulse as the change in momentum, conservation of momentum in isolated systems, collisions and explosions, and the distinction between elastic, inelastic and perfectly inelastic collisions.
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