Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Having trouble wit this problem

  1. Jan 9, 2004 #1
    please help me!!!!!!

    use the fact that the speed of light in a vacuum is about 3.00*10^8 m/s to determine how many kilemeters a pulse from a laser beam travels in exactly nine hours. answer in units of km

    thanks please help!!!
  2. jcsd
  3. Jan 9, 2004 #2
    Distance = velocity * time

    Convert the hours to seconds and then plug those values into this formula. Your will get an answer in meters. Convert that to Km.
  4. Jan 9, 2004 #3

    ok i solved the problem and i got 9.72 * 10^9 but it turned out to be wrong i converted the hours to seconds and got 32400 and i multiplied it by 3.00*8 and got 9.72810^9 which was converted also to km... and the problem is wrong

    when i was taught i was taught distance=velocity/time
  5. Jan 9, 2004 #4
    There are 32400 seconds in 9 hours. 34200s * 3*10^8m/s = 9.72*10^12 m or 9.72*10^9 Km.

    Whoever taught you that d=V/t taught you wrong. Look at the units. The units on one side of the equation have to equal the units on the other side of the equation just like the quantities.

    Distance is in meters
    Time is in seconds
    Velocity is in meters/second

    [tex] Meters(D) = \frac{meters(V) \cdot seconds(t)}{seconds(V)} [/tex]

    The seconds cancel out leaving just meters on both sides of the equation.

    d=v/t is absurd. Acceleration is v/t. m/s^2
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook