You are on a spaceship traveling at 0.80c with respect to a nearby star. You are

Question

You are on a spaceship traveling at 0.80c with respect to a nearby star. You are sending a laser beam to a spaceship following you, which is moving at 0.50c in the same direction.

a. What is the speed of the laser beam registered by the second ship's personnel according to the classical addition of the velocities?

b. What is the speed of the laster beam registered by the second ship's personnel according to the relativistic addition of the velocities?

c. What is the speed of the second ship with respect to yours according to the classical addition of the velocities?

d. What is the speed of the second ship with respect to yours according to the relativistic addition of the velocities?

please not what equations you used. my teacher is useless. thanks

Explanation / Answer

a.

according to classical physics,

the speed of the laser beam registered by the second ship's personnel=u-v,

u=0.50c,

v=0.80c-c=-0.20c

hence,

the speed of the laser beam registered by the second ship's personnel=0.50c-(-0.20c)=0.70c answer

b.

speed of the laser with respect to the star=(w-x)/(1-wx/c^2),

w=c,

x=0.80c,

speed of the laser with respect to the star(k)=0.20c/(1-0.80c^2/c^2),

=c,

hence,

according to relativistic physics,

the speed of the laser beam registered by the second ship's personnel= (u-k)/(1-uk/c^2)

    =(0.50c-c)/(1-0.50c^2/c^2)

   =c answer

c.

speed of the second shipwith respect to me according to classical physics=t-u

   =0.80c-0.50c

=0.30c moving away

d.

speed of the second shipwith respect to me according to classical physics=(u-t)/(1-ut/c^2)

     =0.30c/(1-0.40c^2/c^2)

    = 0.30c/0.60

    =0.50c answer

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