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1. The problem statement, all variables and given/known data

A box is cubical with sides of proper lengths L1 = L2 = L3 = 2.3 m, as shown in the figure below, when viewed in its own rest frame. This block moves parallel to one of its edges with a speed of 0.89c past an observer.

What is the length of each side as measured by this observer? Assume that the side that the block is moving parallel to is L1.

2. Relevant equations

L = Lp square root(v^2/c^2)

3. The attempt at a solution

so i got the answer to L2 and L3 which are the sides of the cube perpendicular to the direction of travel. However i dont know how to find the length of the parallel side. anybody know why?

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# Homework Help: Relativity and observed length of a moving object

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