Say you were at mission control on Earth. You use radio waves to say "Hello" to an
astronaut on Mars when Mars is 84,000,000
km from Earth. The astronaut hears your "Hello"
280 seconds after you spoke the word. How do
you explain this time lag?

The potential in a region between x = 0 and x = 6.00 m is v = a + bx, where a = 14.0 v and b = -7.30 v/m.

Space-time metric ds2= -dt2+at2dx2+bt2dy2+ct2dz2 (a)how does the area of a rectangle with vertices at ( x=0, y=0, z=0 ), (1,0,0 ), ( 0,1,0 ) and (1,1,0 ) changes with time? (b) if a photon moving in the x direction starts from the origin at t=1, when does it reach x=l? (ds=0 for the trajectory of a photon.) (c) the proper time for a particle is defined by cd=ds. what is the proper time for a particle to move along the trajectory ( x(t)=t, y(t)=0, z(t)=0 ) from t=0 to 1 ? what is the condition on the parameter a so that the velocity of the particle never exceeds the speed of light ?

Idon’t quite understand this problem