# Review Q #2

1. Sep 21, 2010

### TeenieWeenie

Problem solved; thanks Thaakisfox!

1. The problem statement, all variables and given/known data
A race car driver must average 200km/hr for six laps of the race track to qualify for a race. If he averages only 150 km/h for the first two laps, calculate the average velocity he must have over the last four laps in order to qualify.
2. Relevant equations
Vavg = (X2 - X1) / (T2 - T1)

3. The attempt at a solution
Set V average = 200 km/hr.
200 = [150+ 4(v)]/6
1200 = 150+4v
1350/4 = V for last 4 laps?

337.5 km/h per lap for the last 4 laps?

Last edited: Sep 21, 2010
2. Sep 21, 2010

### Thaakisfox

You forgot to multiply the 150 with 2, as the car goes 2 laps with that speed.

3. Sep 21, 2010

### TeenieWeenie

Alrighty. I double checked and ended up with this.

200 km/h = [300km/h + 4(v)] / 6
1200 = 300 +4v
900 = 4v
225 km/h = v per lap needed to average at 200km/h for 6 laps.

Does that sound right?

4. Sep 21, 2010

### Thaakisfox

Yep thats right.

5. Sep 21, 2010

### TeenieWeenie

Sweet! I had a feeling 337.5 was not right.
Thanks for the help Thaakisfox!

Problem solved!