Question

A car passes a not-moving person A at 0.85c moving from left to right. A person B on the car measures the car to 100m long. Person B in the middle of the ship fires two photons, one to a detector in the back of the ship and one in the front. 1. According to person B, how long does it take for each photon to strike detectors.

2. For person A, which photon hit first and what is time difference between events.

3. Person A obtains his own car and moves at 0.6c to the left, how fast is person B's car moving with his frame of reference

Answer 1

1) person B is in the rest frame of ship from he fires photons simultaneously so both photons strikes at same time

t1= t2

and c is the speed of photon

so,

2) person B is moving with 0.85c velocity w.r.t person A

so, For photon moving in left direction person A observe his velocity

so, v=c

and for photon moving right

v=c

so both photon moving with same velocity so they wiill also hit simultaneously.

Actually we observe in every frame of refrance speed of light is same which is postualate of STR

3) Now w.r.t rest peson A is moving with 0.6c to left and B with 0.85c to the right so

relative velocity of them is given by velocity addition law