Suppose you measure an round object to have a diameter of 15 cm (about 6 inches)

Question

Suppose you measure an round object to have a diameter of 15 cm (about 6 inches) while it is rest. According to Special Relativity, if you watch it fly past at 200,000 km/s what shape and size will it appear to you to be?

A. Oblong and pancaked, about 11 cm across n the direction of motion, 15 cm across perpendicular to the motion.

B. Oblong and pancaked, 15 cm across n the direction of motion, and about 11 cm across perpendicular to the motion.

C. Oblong and stretched out, about 20 cm across in the direction of motion, 15 cm across perpendicular to the motion.

D. Spherical, as before, and 11 cm in diameter.

Suppose you measure an object to have a length of 15 cm (about 6 inches) while it is rest.  According to Special Relativity, if you watch it fly past at 200,000 km/s what length will it appear to you to be?

A. About 11 cm

B. About 8 cm

C. About 20 cm

D. The same, about 15 cm

A. About 11 cm

B. About 8 cm

C. About 20 cm

D. The same, about 15 cm

Explanation / Answer

1] This is the case of length contraction. When the object is moved with a speed comparable to speed of light, length is contracted in the direction of motion.

So option A is correct.

2] We know that a contracted length, L = Lo sqrt(1-v^2/c^2) = 15*sqrt(1- (200000/300000)^2) = 11.18 cm

option A is correct

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