# Thread: physics - missing variables?

1. ## physics - missing variables?

I feel like there are missing variables to this problem, which is where i'm getting stuck. I feel as if i might need to enter in dummy values to make the problem work?

You drive on Interstate 10 from San Antonio to Houston, half the time at 69 km/h and the other half at 97 km/h. On the way back you travel half the distance at 69 km/h and the other half at 97 km/h. What is your average speed (a) from San Antonio to Houston, (b) from Houston back to San Antonio, and (c) for the entire trip? (d) What is your average velocity for the entire trip?

2. $\displaystyle velocity=\frac{distance}{time}$

Let half of the time=t

$\displaystyle 69=\frac{d_1}{t}$

$\displaystyle 97=\frac{d_2}{t}$

Average Speed on the way there is total distance, divided by total time, which is $\displaystyle \frac{d_1+d_2}{2t}=\frac{1}{2}\frac{d_1+d_2}{t}=\f rac{1}{2}(69+97)=83$

Let half of the distance=d

$\displaystyle 69=\frac{d}{t_1}$

$\displaystyle 97=\frac{d}{t_2}$

Average Speed on the way back is again total distance traveled divided by total time which is $\displaystyle \frac{2d}{t_1+t_2}$

You can work that one out, and again do something similar for average speed of the whole trip

Average velocity for the whole trip is 0 since you the displacement=0 (you end up where you started)

3. Originally Posted by massid
I feel like there are missing variables to this problem, which is where i'm getting stuck. I feel as if i might need to enter in dummy values to make the problem work?

You drive on Interstate 10 from San Antonio to Houston, half the time at 69 km/h and the other half at 97 km/h. On the way back you travel half the distance at 69 km/h and the other half at 97 km/h. What is your average speed (a) from San Antonio to Houston, (b) from Houston back to San Antonio, and (c) for the entire trip? (d) What is your average velocity for the entire trip?