Question

A particular star is at a distance of about $8.1\times {10}^{13}km$ from the earth. Assuming that the light travels at $3\times {10}^{8}m/sec$, find how long does light take from that star to be reach the Earth.

Answer 1

Distance=$8.1\times {10}^{13}km$

$=8.1\times {10}^{13}{10}^{3}m$

speed$=8.1\times {10}^{16}m$

$Time=\frac{dis\tan ce}{speed}=\frac{8.1\times {10}^{16}}{3\times {10}^8}$

$=\frac{8.1}{3}\times {10}^8$

$=2.7\times {10}^8$ sec.