# Homework Help: Relativity and angular speed

1. Sep 14, 2008

### briteliner

1. The problem statement, all variables and given/known data

You point a laser flashlight at the moon producing a spot of light on its surface. At what minimum angular speed must you sweep the laser beam in order for the light spot to streak across the moon's surface with speed v>c? Why can't you transmit information between research bases on the moon with the flying spot?

2. Relevant equations

3. The attempt at a solution
I figure I need to find an angle but I don't get how since there is not much info given in the problem

2. Sep 14, 2008

### Irid

It's probably assumed you know the distance to the Moon d. Then just find the angular velocity for the spot to travel at the speed of light c.

3. Sep 14, 2008

### briteliner

Ok so I get that w=csin(theta)/d but I still don't have an angle

4. Sep 14, 2008

### Irid

You don't need any angle, just assume \theta = 90 deg for the greatest angular speed.

5. Sep 14, 2008

### briteliner

But how can that be right? C/d just gives me .789 rad/s

6. Sep 14, 2008

### Irid

awesome, right?