# Homework Help: Physics 20 - Word Problems

1. Sep 11, 2010

### Blaz3r

1. The problem statement, all variables and given/known data

If a plane can travel 2.00 x 10^3 km in 3.00 hours, what is its velocity in m/s?

2. Relevant equations

3. The attempt at a solution

V =
d = 2.00 x 10^3 km
t = 3.00h

V = 2.00 x 10^3 km / 3.00h

V = 2000km / 3.00h

V = 666.67km/h

666.67 kilometers = 666 670 meters - 666.67 hours = 2 400 012 seconds
I'm not sure what to do at this step changing it to m/s

V = ?m/s

2. Sep 11, 2010

### Staff: Mentor

When you are converting between different units remember that you can always multiply by factors of 1. E.g.

$$\frac{1 min}{60 s}=1$$

If you pick your factors of 1 correctly you can get the units you don't want to cancel out and just leave the units you do want. E.g.

$$120 s = 120 s \; 1 = 120 s \frac{1 min}{60 s} = 2 min$$

Notice how the s on top in the original units cancels out the s on bottom from the factor of 1, leaving only min from the factor of 1.

3. Sep 11, 2010

### Blaz3r

I still don't understand.Are you converting into minutes? I converted into minutes which is 160minutes, do I take my m/160minutes to get my final answer of m/s?

4. Sep 11, 2010

### Staff: Mentor

You have km/h and you want m/s so you need a factor which gives you m on top and cancels out the km, and you need another factor which gives you s on top and cancels out the h. Can you figure out what those factors are?