• Support PF! Buy your school textbooks, materials and every day products via PF Here!

Special Relativity with 2 light beams moving towards each other

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?
 

Dick

Science Advisor
Homework Helper
26,258
618
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.
 

Want to reply to this thread?

"Special Relativity with 2 light beams moving towards each other" You must log in or register to reply here.

Related Threads for: Special Relativity with 2 light beams moving towards each other

Replies
2
Views
1K
Replies
2
Views
1K
  • Posted
Replies
16
Views
3K
Replies
64
Views
4K
Replies
3
Views
477
  • Posted
Replies
4
Views
406

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving
Top