The speed of light in a vacuum is ##2.998 xx 10^8 “m/s”##. (a) What is its speed in kilometers per hour (km/h)? (b) What is its speed in miles per minute (mi/min)?

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    For part (a): ##c = 1.079 * 10^(9)”km/h”## For part (b): ##c = 1.118 * 10^7″mi/min”##

    To solve this problem you need to be familiar with several conversion factors. More specifically, you need to know that

    ##”1 km” = 10″”^3″m”##

    ##”1 h” = “60 min” ” “##and ##” “”1 min” = “60 s”##

    ##”1 mile” = “1.609344 km”##

    SO, for part (a), you need to go from meters to kilometers and from seconds to minutes, then to hours.

    ##2.998 * 10^(8)color(red)(cancel(color(black)(“m”)))/color(red)(cancel(color(black)(“s”))) * “1 km”/(10^3color(red)(cancel(color(black)(“m”)))) * (60color(red)(cancel(color(black)(“s”))))/(1color(red)(cancel(color(black)(“min”)))) * (60color(red)(cancel(color(black)(“min”))))/(1color(red)(cancel(color(black)(“h”)))) = 10792.8 * 10^(5)”km/h”##

    Rounded to four , the number of sig figs you gave for the speed of light in meters per second, the naswer will be

    ##c = color(green)(1.079 * 10^(9)”km/h”)##

    Now for part (b). Now you need to go from meters to kilometers, then to miles, and from seconds to minutes.

    ##2.998 * 10^(8)color(red)(cancel(color(black)(“m”)))/color(red)(cancel(color(black)(“s”))) * (1color(red)(cancel(color(black)(“km”))))/(10^3color(red)(cancel(color(black)(“m”)))) * “1 mile”/(1.609344color(red)(cancel(color(black)(“km”)))) * (60color(red)(cancel(color(black)(“s”))))/”1 min” = 111.77 * 10^(5)”mi/min”##

    Once again, round the answer to four sig figs

    ##c = color(green)(1.118 * 10^7″mi/min”)##

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