A train is moving at constant velocity to the right when bolts of lightning stri

ID: 1599229 • Letter: A

Question

A train is moving at constant velocity to the right when bolts of lightning strike the ground near its front and back. Alive, standing on the dirt at the midpoint of the flasses observes that the light from the two flashes arrives simultaneously, so she says the two strikes must have occured simultaneously. Bob, meanwhile, is sitting aboard the train, at its middle. He passes by Alive at the moment when Alice later figures out that the flashes happened. Later he receives flash 2, and then flash 1. He infers that since both flashes traveled half the length of the train, flash 2 must have occured first. How can this be reconciled with Alice's belief that the flashes were simultaneous? Problem 4.

Explanation / Answer

Considering the second flash

it reaches the observer with a speed c+v where

c is the speed of light for lightening and v is the speed of train moving the the same direction

Whereas

for first flash

it reaches the observer with a speed of c-v

Since they both cover same distance = half the length of train

Using

t = d/s

For second flash

t2 = d/(c+v)

For first flash

t1 = d/(c-v)

Hence clearly

t1>t2

So its due to difference in their frame of refrence

Still for Alive and moving for Bob

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A train is moving at constant velocity to the right when bolts of lightning stri

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