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In traditional Newtonian thinking, if a runner moving at 3 m/s throws a ball forward at 10 m/s, the ball's speed relative to the ground should be 13 m/s. How does relativity treat the speed of light emitted from a moving source?
AThe speed of the source is simply added to the speed of light
BThe speed of the emitted light is not increased by the speed of its source
CThe speed of light becomes negative if the source moves backward
DThe speed of light doubles regardless of the source's speed
Answer & Solution
Correct answer: B. The speed of the emitted light is not increased by the speed of its source
1. Everyday velocities add together, so a thrown ball's speed combines with the runner's speed.
2. Relativity theory instead states that the speed of a moving light source is not added to the speed of the emitted light.
3. This preserves Einstein's second postulate, since light must keep the same speed regardless of the source's motion.
4. The speed of light does not become negative or double based on the source's motion either.
5. So light's speed staying unaffected by its source is correct.
_Source: OpenStax Physics (CC BY 4.0), Ch 10 "Special Relativity", section 10.1 Postulates of Special Relativity_
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