Question

Question 174

A particular star is at a distance of about $8.1\times {10}^{13}km$ from the Earth.
Assuring that light travels at $3\times {10}^{8}m$ per second, find how long does light takes from that star to reach the Earth?

Answer 1

The distance between star and Earth = $8.1\times {10}^{13}km=8.1\times {10}^{13}\times {10}^{3}m[\because 1km=1000m]$
Since, light travels at $3\times {10}^{8}m$ per second.
So, time taken by light to reach the Earth
$=\frac{8.1\times {10}^{13}\times {10}^3}{3\times {10}^8}=\frac{8.1\times {10}^{16}}{3\times {10}^8}=\frac{8.1}{3}\times {10}^8=2.7\times {10}^{8}s$