Question

A new unit of length is chosen such that the speed of light in vacuum is unity. What is the distance between the Sun and the Earth in terms of the new unit if light takes 8 min and 20 s to cover this distance ?

• A. 100 unit
• B. 500 unit
• C. 2 unit
• D. 20 unit

Answer 1

The correct option is B 500 unit

Let new unit of length be a.

Speed of light in vacuum $=3\times {10}^{8}m/s$

$=1a/s$

Hence, 1a = 3 x 10${}^8$m

Distance b/w sun and earth $=v\times t$

$=500s\times 3\times {10}^{8}m/s$

$=500a$ ; note: $a$ is new unit