Question

Light travels at a speed of 3.0 x 10⁸ m/s (meters per second). How can you use this information to calculate the time in seconds it takes for light from Promixa Centrauri to reach Earth? How many seconds does it take based on this information? Write your answer in scientific notation.

Answer 1

$\begin{gathered} d=v\cdot t \\ \text{Where:} \\ d=\text{distance} \\ v=\text{velocity} \\ t=time \end{gathered}$

Promixa Centrauri is 4.244 ly from earth so:

$4,244ly\times\frac{9.46\times10^{12}\operatorname{km}}{1ly}=4.014824\times10^{13}\operatorname{km}$

Light travels at a speed of 3.0 x 10⁸ m/s so:

$3.0\times10^8\cdot\frac{m}{s}\cdot\frac{1\operatorname{km}}{1000m}=300000\cdot\frac{km}{s}$

Therefore:

$\begin{gathered} d=v\cdot t \\ \text{Solving for t:} \\ t=\frac{d}{v} \\ t=\frac{4.014824\times10^{13}}{300000}\approx1338\times10^5s \end{gathered}$