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## Homework Statement

Relative to the rest frame, the trajectory of a space ship is:

[tex]x=vt[/tex]

[tex]y=y_0[/tex]

An observer at:

[tex](x,y)=(0,0)[/tex]

wants to send a photon to hit the spaceship at:

[tex](x,y)=(0,y_0)[/tex]

a) When and in what direction must the observer send the photon?

b) In the frame of the spaceship, what is the angle between the spaceship and the photon's velocity?

## Homework Equations

Basic velocity to distance relations. Possibly Lorentz transformation?

## The Attempt at a Solution

\a) Well, the observer is trying to send a photon from (x,y)=(0,0) to (x,y)=(0,y

_{0}); therefore he muse send it in the +y-direction. The time it takes the photon to reach (x,y)=(0,y

_{0}) is:

[tex]t=\frac{y_o}{c}[/tex]

Since the spaceship is moving in the +x-direction at speed v, the observer must send the photon when the spaceship is at:

[tex]x=vt=\frac{-vy_o}{c}[/tex]

b)This part is hard and I have made a few arguments that lead to different paths:

- The speed of the spaceship in the spaceship's frame is zero, then how could there be an angle?
- When the photon strikes the spaceship, the photon only has a y velocity while the spacecraft has only a x velocity. Therefore, the angle is 90 degrees.