# Motion problem

• Jan 18th 2007, 07:53 PM
crazirani
Motion problem
Hi everyone,

How would I solve this please? Thanks.

Janet drove for 30 miles at 30 miles per hour and the remaining 30 miles at 60 miles per hour. What is her average rate of speed?
• Jan 18th 2007, 07:58 PM
ThePerfectHacker
Quote:

Originally Posted by crazirani
Hi everyone,

How would I solve this please? Thanks.

Janet drove for 30 miles at 30 miles per hour and the remaining 30 miles at 60 miles per hour. What is her average rate of speed?

I think average rate is defined with the formula,
$\frac{\mbox{Total Distance}}{\mbox{Time}}$

The time wasted in the first part was,
$\frac{30}{30}=1\mbox{ hour}$
The time wasted in the second part was,
$\frac{30}{60}=.5\mbox{ hours }$

The total distance was,
$30+30=60$

Thus, the average speed was,
$\frac{60}{1.5}=\frac{60}{\frac{3}{2}}=\frac{60}{1} \cdot \frac{2}{3}=40$ miles per hour.
• Jan 18th 2007, 08:02 PM
crazirani
Thank you very much.
• Jan 18th 2007, 09:28 PM
CaptainBlack
Quote:

Originally Posted by crazirani
Hi everyone,

How would I solve this please? Thanks.

Janet drove for 30 miles at 30 miles per hour and the remaining 30 miles at 60 miles per hour. What is her average rate of speed?

Average speed=(total distance)/(total time)

30 miles at 30 miles per hour took 1 hour,
30 miles at 60 miles per hour took 1/2 hour.

So average speed=(60 miles)/(1.5 hours)=40 miles per hour.

RonL
• Jan 18th 2007, 10:36 PM
crazirani
Thanks CP.

I just used another problem similar to this one. Thanks!