GREPhysics.NET: GR8677 #70

GR8677 #70

Problem

GREPhysics.NET Official Solution

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

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

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Saybrook
2014-09-24 18:51:52

Saybrook
2014-09-24 18:54:17

Nevermind this is exactly what Yosun wrote; I just glanced at it.

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Mindaugas
2007-09-28 08:00:11

Answer A is also the only one which is smaller than 4 m.

neon37
2010-11-03 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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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

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