A star is 8.1 × 10¹³ km away from the earth. Suppose light travels at the speed of 3.0 × 10⁵ km per second… · ABC26GN3610

Subject: General Aptitude · Chapter: Time and Distance · Exam: R.R.B. 2005

A star is $8.1 \times 10^{13} \mathrm{km}$ away from the earth. Suppose light travels at the speed of $3.0 \times 10^{5} \mathrm{km}$ per second. How long will it take the light from the star to reach the earth?
(a)$7.5 \times 10^{3}$ hours
(b)$7.5 \times 10^{4}$ hours
(c)$2.7 \times 10^{10}$ seconds
(d)$2.7 \times 10^{11}$ seconds
Answer
Answer (as printed): B
Explanation
Required time $=\left(\frac{8.1 \times 10^{13}}{3.0 \times 10^{5}}\right)$ seconds $=2.7 \times 10^{8} \mathrm{sec}$ $$=\left(\frac{2.7 \times 10^{8}}{60 \times 60}\right) \mathrm{hrs}=7.5 \times 10^{4} \mathrm{hrs} .$$

Explanation as extracted from the printed page; notation may be imperfect.

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