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GR8677 #70
Problem
 GREPhysics.NET Official Solution Alternate Solutions

Special Relativity$\Rightarrow$}Length Contraction

One deduced the approximate value of $\gamma$ in Problem 69 (as well as the equation for length contraction). Thus, $4=\gamma L_{moving}\Rightarrow L_{moving}=4\times 3/5=12/5=2.4$. This is choice (A).

Alternate Solutions
 Saybrook2014-09-24 18:51:52 Isn't it this simple? (rest length of car)/(relative length of car)=(rest length of garage)/x where you solve for x which is the relative length of the garage in the car's rest frame. 5/3=4/x => x=12/5=2.4Reply to this comment
Saybrook
2014-09-24 18:51:52
Isn't it this simple?
(rest length of car)/(relative length of car)=(rest length of garage)/x
where you solve for x which is the relative length of the garage in the car's rest frame.
5/3=4/x => x=12/5=2.4
 Saybrook2014-09-24 18:54:17 Nevermind this is exactly what Yosun wrote; I just glanced at it.
Mindaugas
2007-09-28 08:00:11
Answer A is also the only one which is smaller than 4 m.
 neon372010-11-03 12:13:13 Yep! think about the term "length contraction" and relative velocity and reference frames. In the car's reference frame, the garage is moving. So the length of the garage has to contract, which means smaller than 4, and A is the only one.

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