Paul and ivan are riding a tandem bike together. they’re moving at a speed of 5 meters/second. paul and ivan each have a mass of 50 kilograms. what can paul do to increase the bike’s kinetic energy? a. he can let ivan off at the next stop. b. he can pedal harder to increase the rate to 10 meters/second. c. he can reduce the speed to 3 meters/second. d. he can pick up a third rider.

The formula is Ke = 1/2 m v^2
The two of them together have a Ke of mv^2. So you either increase m or v. That's what makes the problem difficult. He can do D or B. We have to choose.

A is no solution. The Ke goes down because Paul loses Ivan's mass.
C is out of the question 3 meters/sec is a big reduction from 5 m/s. So now what do we do about B and D?

The question is what does the third person add. The tandoms I've peddled only allow for 1 or 2 people to add to the motion. So the third person only adds mass. He does not have a v that he is contributing to. To say that he is going 5m/s is true, but he's not contributing anything to that motion.

I pick B, but it is one of those questions that the correctness of it is in the head of the proposer. Be prepared to get it wrong. Argue the point politely if you agree with me, but back off as soon as you have presented your case.

B <<<< answer. 

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