Relativity - Professor in spaceship examning students

[azatkgz]

And also check this one.

Homework Statement

A physics professor on the Earth gives an exam to her students.who are in the spacecraft traveling at a speed v relarive to the Earth.The moment the craft passes the professor,she signals to start of the exam.She wishes her students to have time interval $$T_0$$( spacecraft time)to complete the exam.Find the time interval T(Earth time) she should wait before sending a light signal telling them to stop.

The Attempt at a Solution

When in spacecraft $$T_0$$ for professor
$$T'=\frac{T_0}{\sqrt{1-\frac{v^2}{c^2}}}$$
$$T=T'-\frac{vT'}{c}=T_0\sqrt{\frac{1-v/c}{1+v/c}}$$

 

[MathematicalPhysicist]

seems alright by me, youv'e substracted the time it would take the signal to get to the spacecaraft from the overall time for the exam in the Earth's system.
nice work.