Actual time of the bulb is fired.

Question

A flash bulb is located at a distance 30km from an observer. The bulb is fired and the observer sees the bulb at 13:00 hrs. What is actual time that the bulb is fired?

Answer 1

In order to determine the time that the bulb was fired we need to know the time it took for the light from the bulb to travel the 30km distance to the observer.

To do so, we need to know the speed of light. Most often, physics textbooks use the approximation:

speed of light = 3.00 x 10⁸ m/s

Since our distance is in km, it is helpful to convert the speed of light to km/s.

speed of light = 3.00 x 10⁵ km/s (divide 3.00 x 10⁸ by 1000)

Using the formula: v = d/t, solve for t.

t = d/v

plugging in what we know....

t = 30 km / 3.00 x 10⁵ km/s = 0.0001 s

This means that the bulb was fired 0.0001s prior to the observer seeing the flash at 13:00.

FINAL ANSWER

Hope this is helpful!