Suppose the spaceship in the previous example is approaching the Earth at half the speed of light and shoots a canister at a speed of 0.750c.

(a) At what velocity will an Earth-bound observer see the canister if it is shot directly towards the Earth?

(b) If it is shot directly away from the Earth? (See Figure 28.17.)

Strategy
Because the canister and the spaceship are moving at relativistic speeds, we must determine the speed of the canister by an Earth-bound observer using relativistic velocity addition instead of simple velocity addition.

u' = 0.75c V = 0.50c Canister toward Earth u'= -0.75c v = 0.50c Canister away from Earth