Have You Read Up On Your Einstein?

Classical Mechanics Level 3

Einstein is riding in a space-ship in at a constant speed of 67% the speed of light. His friend, Bose, is riding (also constantly) at 86% the speed of light. Their paths are parallel, and they are going perfectly straight. Bose, as a prank on Einstein, takes out his laser-gun, and fires it at Einstein when he is 180,000 kilometers ahead of him, at just the right angle so that it goes directly into Einstein's eyes. From Einstein's perspective, what is the speed of the light at the exact moment it hits his eyes?

Details and assumptions

Assume that light travels at 300,000,000 meters per second, and that it is not affected by the space-ship's windshield.
The universe that Einstein and Bose are in is relativistic.
The space-ships have no gravity, nor does anything else in the universe.

The answer is 300000000.

6 solutions

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Poonardeep Singh
Feb 21, 2014

One of the laws of relativity states that the speed of light is the ultimate speed. it remains constant everywhere.

so i had the correct answer but this website wont accept my answer in scientific notation. i wrote 3E-8 m/s . and it didnt accept. HURRAH!

Syed Roshaan - 7 years ago

ainstain and the light have the direction at 90 angle i think that's why the relative speed will remain same

Abhijit Bhowmik - 7 years, 2 months ago

i think it is not because of right angle. but because of relativity principle, in simple language we might think einstein himself travelling at high speed must see the light relatively slower and hence the speed should be less, but actually according to relativity the time also slowed down in einstein's frame compensating for the speed.

Vishal Sharma - 7 years, 2 months ago

Finn Hulse
Feb 9, 2014

Special theory of relativity... Light is constant for any observer. For those who did the actual math and treated light as a vector, that sucks. ;)

Nice one man!

Archiet Dev - 7 years, 4 months ago

Jeric Garrido
May 13, 2014

The Second Postulate of Special Relativity says that the speed of light in free space doesn't depend on the motion of the observer or the observed, hence the speed of light is invariant. Thus you drop all of the facts given and just answer the speed of light.

Raiyun Razeen
Feb 20, 2014

The speed of light is constant everywhere.

So, the answer is 300,000,000 m/s.

don't you guys think the speed of light is exactly 299792.458 km/s or exactly 186282 miles 2096 feet and 5 21/127 inches per second

Faiz Hassan - 7 years, 2 months ago

According to the question it says "Assume that light travels at 300,000,000 meters per second....." so it is reasonable to say that 299192458 m/s is not the answer.

Kelvin Tan Jin Loong - 6 years, 7 months ago

Aditya Sarwate
Feb 20, 2014

Since speed of light will be always constant..Hence the answer is 3*10^8 m/s...

speed of light remains the same as it does no get its speed increased by a contact speed hence it remains the same 300000000 m/s or 3*10^8 m/s.

Sai Datta - 7 years, 3 months ago

Akshay Kadu
Feb 26, 2014

Speed difference between Einstein and Bose is 300000000 * (86-67)/100 = 57000000 speed of light = 300000000 Since bose fired it at right angle. By pythagorus theorem final speed : $\sqrt{300000000^{2}+57000000^{2}} = 305366992$

This is incorrect. You got lucky due to rounding. See Finn's solution.

Ahaan Rungta - 7 years, 3 months ago

Have You Read Up On Your Einstein?

The answer is 300000000.

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