Question

The apparent wavelength of the light from a star, moving away from the earth is `0.01%` more than its real wavelength. The speed of the star with respect to earth is
A. `10 km//s`
B. `15 km//s`
C. `30 km//s`
D. `60 km//s`

Answer 1

Correct Answer - C
`(Delta lambda)/(lambda) = (v)/(c ) rArr (0.01)/(100) = (v)/(3 xx 10^(8))`
`v = 3 xx 10^(4) m//s = 30 km//s`