Question

A relativistic ‘runner’, carrying a 20 meter pole, runs by an observer with a speed which causes the pole to appear 12 meters in length to the observer.

(a) What is the runner’s speed relative to the observer?

====> runner's speed is 0.8c

Two observers, A and B, with synchronous clocks are positioned at the front and back doors of a barn that is 15 meters in length. The back door of the barn is closed and the front door is open. The runner runs with his pole through the open front door. A closes the door as soon as the pole is inside and notes the time on his clock. At the back of the barn B opens the door just before the pole hits it and also notes the time. Later A and B compare their times and find that tB> tAand conclude that the pole was ‘enclosed’ in the barn.

(b) What is the length of the barn as seen by the runner?

(c) How does the runner explain the events as witnessed by A and B?

Answer 1