Question

You can see a clock in a spaceship moving past you at 90 percent of the speed of light. according to you, how much time would pass while the clock in the spaceship ticked through one minute?

Answer 1

$t = \gamma\tau, \textnormal{ where } \gamma \equiv \frac{1}{\sqrt{1-\frac{v^2}{c^2}}}, \textnormal{ }\tau \textnormal{ is the proper time 60s} \\ t = \frac{60s}{\sqrt{1-0.9^2}} = 137.65s \textnormal{ } (5 s.f.)$