How many nanoseconds does it take light to travel 2.00 km in vacuum?

Answer 1

One 'rule of thumb' that many of us oldtime engineers carry in our decomposing

mental toolboxes is: 1 foot = 1 nanosecond. Since you asked, I'll calculate it now,

and see how close it is:

Speed of light in vacuum = 299,792,458 meters per second.

Use 1 meter = 3.28084 feet

Speed of light = 983571000 feet per second.

Speed of light = 0.98357+ foot per nanosecond

"1 foot = 1 nanosecond" is within 1.65 percent of being accurate.

2.5 feet (in vacuum) takes 2.5418 nanoseconds (rounded)

Answer 2

Way back in Engineering school, I vivdly recall one of my profs telling us that
we could get awfully close if we use [ 1 nanosecond = 1 foot].

(This was very interesting to all of us at that time, since the foot, the nanosecond,
and light itself had been invented only a short time earlier.)

But I digress. Let's examine our thumb closely and see if this rule holds water:

-- Speed of light in vacuum: 299,792,458 meters per second = 983,571,000 feet per second (rounded)

-- Feet per nanosecond: 0.983571

-- Compared to 1 ft/ns : 1.64% low.

This proved to be an excellent rule of thumb since, in our Engineering school, lacking
any test equipment, anything within an order of magnitude was as good as "right on".

To put a somewhat finer and more modern point on it, today we would say that
in vacuum, light takes 2.0334 ns to cover a distance of 2 feet.

Answer 3

Just use the equation:distance = speed x time

Solving for time:

time = distance / speed

Note 1: The speed of light is 300 million meters/second.

Note 2: A second has a billion (10 to the power 9) nanoseconds.

Answer 4

Light travels at about 300,000 km/sec. Time =distance/speed = 2km/300000 = 1/150000 second = 1/0.15 nanosecond = 6.66 nanoseconds