The distance of a galaxy from the earth is 5.6 x 10²⁵m. Assuming the speed of light to be 3 x 10⁸ ms-1, find the time taken by light to travel this distance.

Hint —

$\text{Time taken} =\dfrac{\text{distance travelled}}{\text{speed}}$

Given,

$\text{Time taken} =\dfrac{\text{distance travelled}}{\text{speed}}$

distance = 5.6 x 10²⁵m

speed = 3 x 10⁸ ms^-1

Substituting the values in the formula above we get,

$\text{Time taken} =\dfrac{5.6 \times 10^{25}}{3 \times 10^8} \\[0.5em] \Rightarrow \text{Time taken} ={1.87 \times 10^{17}} s \\[0.5em]$

Therefore, time taken by light = 1.87 x 10¹⁷s.