A question of C7 speed
 

It's another lovely day driving your C7. Ahead of you is a hill. It's one mile up the hill, and one mile down the other side. If you average 30 mph going up the hill (one mile), how fast would you have to drive down the other side in order to average 60 mph over the entire two miles?

30 + 90 = 120 /2 = 60

90 mph

At first I thought 90 but then figured it had to be a brain teaser. If you travel 30mph for 1 mile, it takes 2 minutes. To average 60 mph over 2 miles, it takes 2 minutes. So...if you've already taken up the 2 minutes in the first mile, there's no way to average 60mpg over 2 miles. Correct?

Ken has it right. Time really has no bearing. 90MPH is correct.

I feel like I'm reading a story problem from third grade. If one train leaves from New York doing 60 mph and another train leaves from Chicago going 90 mph on the same track heading toward each other where will they crash?

Washington

Flenn is correct. To average 60 miles per hour for two miles, you have to do the entire distance in two minutes. Time is everything.

Yes you are correct. If you drive up the hill at 30 mph and down the hill at 120 you have travelled 2 miles in 2.5 minutes which is only 48 mph average.

The faster you go on the down side the closer you get to 60 but technically even at the speed of sound you'd still be slightly under 60 mph average.

I giving this quiz to my engineering staff tomorrow...what a great problem.

So travelling at 30 mph over the 1st mile, we already acknowledged that it would take 2 minutes to cover the 1st mile. Assuming that you can instantly accelerate from 30 to 90 mph at the end of the 1st mile, it will take 0.67 minutes to cover that 2nd mile, so you've traveled the total of 2 miles in a total of 2.67 minutes.

2 miles/2.67 minutes X 60 minutes/hr = 44.9 mph over those 2 miles

I may be missing something but there isnt any mention of time only average mph. Since time isnt in the equation 90 would be the answer at least in my mind :flag:

Speed (velocity) by definition is distance traveled over a given time period...thus for our example measured in miles/hr. Without a time factor, there is no speed calculation...only distance. Hope that helps

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LOVE IT!!

That was THE best joke of the day!

Way to go KenHorse!
That was the answer to the riddle that was asked!

Yup, the crash is definitely in Washington DC. That is the correct answer!

LOL :thumbs:



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Yes but some of the posts mentioned 2 minutes to travel the distance and nowhere in the op's statement that there is a 2 minute time limit to travel the distance I think you all are overthinking a very simple question , you are traveling 2 miles you avg 30 mph for the first mile what speed do you need to travel in the other mile to avg 60 mph for the 2 miles. where the 2 minutes come from is beyond me :flag:

So in our example...you are given average spd and distance (60mi/hr...2 mi). You calculate time as t=d/v which converting 60 min = 1 hr: t = 2min. If you know your first 1 mile was traveled at 30mi/hr...you calculated time for that distance iand you will find that t=2 mins for mile 1. This leaves you 0 mins to travel the next mile such that your average speed or time required to hit the average speed is 60mph or 2 mins.

Geez, I thought he meant Washington State.

How about if I was a passenger for the 2nd mile in a 1985 DeLorean driven by Dr. Emmett Brown - since the 30 mph average speed in mile 1 is only an average, we could exit that mile going 88 mph and complete the second mile in 0 seconds and thus average 60 mph.

Well, even the Delorean can't exceed the speed of light which means the best you can do is cover the second mile in .0000053 seconds. Still not enough to get you to a 60mph average...

Oh for fks sake...

It takes EXACTLY TWO minutes to travel TWO miles at 60miles per hour.

To average 60 miles per hour over two miles takes EXACTLY two minutes.

If you have a velocity of 30 miles per hour for the first mile it takes TWO miinutes to cover the distiance.. Since 30 is 1/2 of 60....

Therefore, it doesn't matter how fast you go, you can't do it... Your two minutes are up...

As usual Ken is wrong...

Now if you went up the hill at 90................:auto: