Multiple choice

A star is $8.1 \times 10^{13} km$ away from the earth. Suppose right travels at the speed of $3.0 \times 10^5 km$ per second, how long will it take light from the star to reach the earth?

  1. $7.5 \times 10^3 hrs$
  2. $7.5 \times 10^4 hrs$
  3. $2.5 \times 10^{10} sec$
  4. $2.7 \times 10^{11} sec$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Time = Distance / Speed = (8.1 * 10^13) / (3.0 * 10^5) = 2.7 * 10^8 seconds. Convert to hours: (2.7 * 10^8) / 3600 = 2.7 * 10^8 / (3.6 * 10^3) = 0.75 * 10^5 = 7.5 * 10^4 hours.

AI explanation

Using the formula time equals distance divided by speed, the time in seconds is 8.1 x 10^13 km divided by 3.0 x 10^5 km per second, which equals 2.7 x 10^8 seconds. To convert this time to hours, divide by 3600, yielding 2.7 x 10^8 divided by 3.6 x 10^3. The time taken by the light is 7.5 x 10^4 hours.

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