Old Auto

An old auto is to drive a stretch of 2 miles, up and down a hill. Because the auto is so old, you cannot drive the first mile (the ascent) faster than 15 miles per hour.

old-auto-drive-up-down-hill

How fast do you have to drive the second mile (going down the hill) in order to get an average speed of 30 miles per hour?

Answer

There is no way to get an average speed of 30 mph (miles per hour).

If your average speed for the 2 miles stretch must be 30 mph, you should do it in 4 minutes. During the ascent, you would have already taken 4 minutes to travel 1 mile at 15 mph.

Since you have taken 4 minutes to go up the hill, you will need to take 0 seconds to travel the 1 mile descent in order to get an average speed of 30 mph. This is not possible.

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  • Makala

    My guess would that the ascent is 15 mph so the descend would have to be 45 mph. Because 15 + 45 = 60. 60 / 2 = 30. 30 is the average, so it would make sense that the descend is 45 mph.

    • Wes Sturdevant

      That is my thought though I’m not sure if f=ma and all that physics works that way or not. It could be more complex or i may be overthinking it as 45 seems to be my first easy answer. do you have to log in to see the answer or what? –

      confused Okay got the answer and does make sense, it’s harder than it looked as i didn’t read all the question apparently, I hate directions… lol