Observer A sees a pendulum oscillating back and forth in a relativistic rocket and measures its period to be TA. Observer B moves along with the rocket and measures the period of the
Pendulum to be TB. What is true about these two time measurements?

Question

Observer A sees a pendulum oscillating back and forth in a relativistic rocket and measures its period to be TA. Observer B moves along with the rocket and measures the period of the
Pendulum to be TB. What is true about these two time measurements? 
A) $T _ { A } = T _ { B }$
B) $T _ { A } > T _ { B }$
C) $T \mathrm {~A} < \mathrm { T } _ { \mathrm { B } }$
D) $T$ A could be greater or smaller than $T _ { B }$ depending on the direction of the motion.

Quizplus · Accepted Answer

According to the theory of relativity, time dilates (or slows down) from the perspective of a stationary observer watching a moving clock. Therefore, Observer A, who is stationary relative to the moving rocket, would measure the pendulum's period $T_A$ to be longer than $T_B$, the period measured by Observer B who is moving with the rocket.

Observer a Sees a Pendulum Oscillating Back and Forth in a Relativistic