Question

Two particles approach each other with a velocity of 0.9 c. What is their relative velocity as observed by A?

(a) 0.9 c

(b) 0

(c) 0.99 c

(d) 0.94 c

The question was posed to me during an interview.

My doubt is from Law of Addition of Velocities in section Ultrasonics & Relativity of Engineering Physics I

Answer 1

The correct choice is (c) 0.99 c

To explain I would say: u’ = 0.9c, v = 0.9c

ux = \(\frac{u^{‘}+v}{1+\frac{u^{‘}v}{c^2}}\)

= 1.8c/1.81

= 0.99 c.