009A Sample Final 2, Problem 9

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A plane begins its takeoff at 2:00pm on a 2500-mile flight. After 5.5 hours, the plane arrives at its destination. Give a precise mathematical reason to explain why there are at least two times during the flight when the speed of the plane is 400 miles per hour.

Intermediate Value Theorem
        Let    be a continuous function on the interval    and
        without loss of generality, let  

       Then, for every value    where  

       there is a value     in    such that  


Step 1:  
On average the plane flew
Step 2:  
In order to average this speed, the plane had to go from 0mph, up to full speed, past 454.5mph, and then it had to go back down to 0mph to land.
This means that there will be at least two times where the plane of the speed is 400mph by the Intermediate Value Theorem.

Final Answer:  
       See above.

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