Who Is The Observer?

Classical Mechanics Level 2

Two space shuttles are in co-linear movement, and they will collide one against the other.

If the space shuttle A is traveling with a velocity of $0.7c$ and the space shuttle B is traveling with a velocity of $0.8c$ . If you are in Shuttle A , what is the velocity of B relative to you?

Definition: $c$ is the speed of light.

0.1c

c

0.96c

1.5c

2 solutions

Victor Paes Plinio
Apr 11, 2016

The Einstein's formula to do it is:

$\frac{v_1 + v_2}{1+v_1\cdot v_2/c^2}$

Make the substitutions:

$\frac{0.7c + 0.8c}{1+0.7c\cdot 0.8c/c^2}=\frac{1.5c}{1.56}$

It is approximately to $0.96c$ .

You can also use the sense that nothing can be more fast than light, thus a simple sum not solve it totally.

Used the same analogy...

Ayush Choubey - 5 years, 2 months ago

Is there a wiki page in brilliant about this?

Mr Yovan - 5 years, 2 months ago

Hi @Mr Yovan ,

The relevant subject here is special relativity . Unfortunately it seems that the quoted formula is not actually in the wiki. I'm going to be editing this one over the next couple days, so I'll try to add it in there.

Matt DeCross - 5 years, 1 month ago

nice one .....

Umair Siddiqui - 5 years, 2 months ago

A Former Brilliant Member
Apr 14, 2016

Criteria 1: The velocity will not be larger than or equals to 1c.

Criteria 2: The velocity will be larger than the larger one of the velocities of the space shuttles. (In this case it refers to $V_B$ .

Hence, 3 of the 4 options have been eliminated, leaving us with the final option.

those criteria eliminate only 2 of the options (1 and 4). c (option 2) also meets the 2 criteria as it is not larger than 1c and it is larger than Vb

Reginald Micu - 5 years, 1 month ago

Who Is The Observer?

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