CUET Preparation Today
A star is $8.1 \times 10^{13}$ km away from the earth suppose light travels at the sped of $3 \times 10^5$ km/s. How long will it take to lake light from the star to reach the earth? |
$7.5 \times 10^3$ hrs. $7.5 \times 10^4$ hrs. $2.7 \times 10^{10}$ sec. $2.7 \times 10^{11}$ sec. |
$7.5 \times 10^4$ hrs. |
The correct answer is Option (2) → $7.5 \times 10^4$ hrs. $\text{Time} = \frac{\text{Distance}}{\text{Speed}}$
$\text{Time} = \frac{8.1 \times 10^{13}\text{ km}}{3 \times 10^5\text{ km/s}}$
$\text{Time} = 2.7 \times 10^8\text{ seconds}$
Since $1\text{ hour} = 3600\text{ seconds}$, divide your result by 3600
$\text{Time in hours} = \frac{2.7 \times 10^8}{3600}$
$\text{Time in hours} = \frac{2.7 \times 10^8}{3.6 \times 10^3}$
$\text{Time in hours} = 0.75 \times 10^5\text{ hours}$
$\text{Time} = \mathbf{7.5 \times 10^4\text{ hrs}}$
|
