Special Relativity with 2 light beams moving towards each other

Felipe Doria

1. Homework Statement

If one light beam is heading toward you from the right, and another is heading toward you from the left, how quickly from the perspective of the right-moving beam is the left-moving beam approaching it?

1) 0
2) c
3) 1.5c
4) 2c

2. Homework Equations

(v+w) / (1 + cw/c2)

3. The Attempt at a Solution

I tried plugging in c into the equation for both v and w but it gives me (c + c) / (1 + c2/c2) which equals 2c. It is one of the possible answers but I know nothing can go faster than c so I'm thinking the answer is probably c. Am I right? If so, why? If not, what am I doing wrong?

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Dick

Homework Helper
1. Homework Statement

If one light beam is heading toward you from the right, and another is heading toward you from the left, how quickly from the perspective of the right-moving beam is the left-moving beam approaching it?

1) 0
2) c
3) 1.5c
4) 2c

2. Homework Equations

(v+w) / (1 + cw/c2)

3. The Attempt at a Solution

I tried plugging in c into the equation for both v and w but it gives me (c + c) / (1 + c2/c2) which equals 2c. It is one of the possible answers but I know nothing can go faster than c so I'm thinking the answer is probably c. Am I right? If so, why? If not, what am I doing wrong?
(c+c)/(1+c^2/c^2) isn't equal to 2c.

"Special Relativity with 2 light beams moving towards each other"

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