Physics help!?

2.00 km x (1 s / 299792.458 km ) x (1 x 10^9 ns / 1 sec) = 6670 ns with 3 sig figs.

note the method...called unit factor method of unit conversion.

idea is this.

1) any number x 1 = that number

2) conversion equalities can be setup to equal 1

3) units cancel same as variables and digits.

example. 20 cm to inches.....

since 2.54 cm = 1 in if we divide both sides by 2.54 cm we get

2.54cm / 2.54 cm = 1in /2.54 cm

1 = 1in /2.54 cm

to convert....

20 cm = 20 cm x 1 = 20 cm x (1in /2.54 cm) = 7.87 inches

note that the cm's have cancelled and we're left with inches.

in the case of cubes, squares, etc,

if we start with

1 = 1in /2.54 cm and cube both sides we get

1^3 = (1in /2.54 cm)^3 but since 1^3 = 1,

(1in /2.54 cm)^3 = 1

example convert 10 ml to in^3

note also that 1 cm^3 = 1 ml

10 ml = 10 ml x (1cm^3/1 ml) x (1 in / 2.54 cm)^3 = 3.94 in^3

ml and cm^3 have canceled and we're left with in^3

very useful process because you can easily see if you should multiply or divide.....

You are off by a zero in the number of nanoseconds in a second -- it is a billion, not a hundred million. Since light travels 3E8 meters in a second (approximately), it will travel a billionth that far in a nanosecond. Since s = vt, and you are given s and v but want t, some trivial algebra gives t = s/v, and you take it from here.

well yo know that velocity is distance divided by time....an dnanoseconds is 10^-9......so set up speed of light = 2 km / time

where time is ur answer in seconds....there for its distance / speed of light.... divide u answer by 100,000,000 to get i nano seconds

distance = rate * time

rate = 299792.458 km/s

distance = 2 km

time = distance / rate