# A question about speed of light

1. Aug 21, 2015

### nirky

If there is a person walking along the road at the speed of 5km/h and a car traveling in the same direction as the person at 60km/h relative to the person. How to calculate their the distance between them?

Also the velocity of light is 186 000 miles per second and what if both object X and Y can travel at 186 000 miles per second but object Y has an head start of 186 000 miles. How far apart would they both be in an hour? Or will there be no difference between them?

2. Aug 21, 2015

### DaveC426913

Insufficient information. They could be adjacent, they could be a mile apart.

You could calculate how far apart they are after a given duration since they passed each other. Is that what you're asking?

They are separating at 55km/h. That's 55,000 metres every 3600 seconds.
Convert that to units of your choice, say metres per second, and multiply by the number of seconds of your desired duration.

c = 186,262mi/s.

Not nitpicking - this will matter in your scenario:
They cannot travel at the speed of light (unless they're photons). But at 186,000mi/s (99.86c), they are still 262mi/s short, so it's OK.

They are travelling at the same speed. After one hour, they will be the same distance - 186,000 miles - apart. Is there a reason you would think otherwise?

Last edited: Aug 21, 2015