# Question: You are standing on the Earth and observe a spacecraft

You are standing on the Earth and observe a spacecraft speeding by with your professor on board.

(a) If both you and your professor are observing your wristwatch, who is measuring the proper time?

(b) Who measures the proper length of the spacecraft?

(a) If both you and your professor are observing your wristwatch, who is measuring the proper time?

(b) Who measures the proper length of the spacecraft?

## Answer to relevant Questions

If an electron has a kinetic energy of 2 keV, could the classical expression for kinetic energy be used to compute its speed accurately? What if its kinetic energy is 2 MeV? Explain. A car accelerating from rest is a noninertial system. Explain the “forces” (and draw the free-body diagram) that the driver uses to explain why a coffee mug on the slippery dashboard might slide “backward.” How does ...Two identical high-speed rockets pass your (inertial) space station. Their pilots each claim that their rocket is 100 m long. You measure the length of rocket A to be 89 m and that of rocket B to be 79 m. Which one is ...A cylindrical spaceship of length 35.0 m and diameter 8.35 m is traveling in the direction of its cylindrical axis (length). It passes by the Earth at a relative speed of 2.44 x 108 m/s. (a) What are the dimensions of the ...How fast must an object travel for its total energy to be (a) More than its rest energy and (b) More than its rest energy?Post your question