# Homework Help: Having trouble wit this problem

1. Jan 9, 2004

### licia589

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

2. Jan 9, 2004

### Jimmy

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.

3. Jan 9, 2004

### licia589

ok...

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

4. Jan 9, 2004

### Jimmy

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

$$Meters(D) = \frac{meters(V) \cdot seconds(t)}{seconds(V)}$$

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