Cracking the SAT Physics Subject Test

when u or v is close to the speed of light that the difference becomes measurable.

Let’s apply the correct formula to our previous example about the spaceship

emitting a pulse of light. With you on the planet and me on the spaceship, u = c.
Naturally, I measure the speed of the light pulse to be v = c, and you would measure
its speed to be

just as Postulate 2 says you must.

Question 14-15

An enemy spaceship of the Empire is traveling toward the planet

Ceti Alpha VI at a speed of 0.4c. The ship emits a beam of

antiprotons at the planet that travel at a speed of 0.5c relative to the

ship.

14. How fast are the antiprotons traveling relative to the planet?


15. If the Empire ship emits a pulse of red light just before its blast
    of antiprotons, with what speed does the red light travel, relative to
    the planet?

Here’s How to Crack It

14. With u = 0.4c and v = 0.5c, the speed of the antiprotons relative to the
    planet is