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A star is 8.1 × 1013 km away from the earth. Suppose light travels at the speed of 3.0 × 105 km per second. How long will it take the light from the star to reach the earth ?
Answer & Solution
Correct Answer:
Option
B
Required time :
$$\eqalign{ & = \left( {\frac{{8.1 \times {{10}^{13}}}}{{3.0 \times {{10}^5}}}} \right){\text{seconds}} \cr & = 2.7 \times {10^8}{\text{ seconds}} \cr & = \left( {\frac{{2.7 \times {{10}^8}}}{{60 \times 60}}} \right){\text{hours}} \cr & = 7.5 \times {10^4}{\text{ hours}} \cr} $$
$$\eqalign{ & = \left( {\frac{{8.1 \times {{10}^{13}}}}{{3.0 \times {{10}^5}}}} \right){\text{seconds}} \cr & = 2.7 \times {10^8}{\text{ seconds}} \cr & = \left( {\frac{{2.7 \times {{10}^8}}}{{60 \times 60}}} \right){\text{hours}} \cr & = 7.5 \times {10^4}{\text{ hours}} \cr} $$
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