Length Contraction Problem for a Rod in a Spaceship

[Skyxplorer]

Homework Statement

A rod has length of 1m. It is moving in a spaceship with velocity 0.4c relative to the earth. The length of the rod measured by an observer in the spaceship will be

(A) 1m

(B) 0.9m

(C) 0.5m

(D) 0.25m

Relevant Equations

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Shoudnt answer be A since for observer in spaceship rod is at rest.

 

[Orodruin]

Yes

 

[Skyxplorer]

Thank you for confirming

 

[DaveC426913]

One might take is as a good assumption, but nowhere do I see it mentioned that the rod is at rest relative to the spaceship.

(In fact, it kind of says "it (the rod) is moving in a spceship" so I wouldn't be too quick with that assumption.)

 

[kuruman]

One might take is as a good assumption, but nowhere do I see it mentioned that the rod is at rest relative to the spaceship.

In fact it clear from the statement that it (the rod) is moving

$\dots$ with velocity 0.4c relative to the earth.

It is safe to assume that the observer is at rest relative to the spaceship, but we are not told the velocity of the spaceship (and observer) relative to the rod.

Answer (B) is consistent with the spaceship being parked on the Earth and the rod passing through two diametrically opposing openings at 0.4c but that's stretching it.