Fine, I'll quote myself with some bits bolded to point out where I know Steven is getting confused.
Quote:
Originally Posted by Kal
This is an old quiz question, a 'Millergram' from Professor Julius Sumner Miller from back in the 60's last century.
Q32: A juggler comes to a foot-bridge of rather flimsy design. He has in hand four balls. The safe load is no more than the juggler himself and one ball. Can he get across the bridge by juggling the balls, always having at most one ball in the hand (and three in the air)?
A: No. A falling ball exerts a force on the hand greater than its own weight.
Rather, a 'thrown' ball exerts greater force than a 'held' one. That is, the additional force equal and opposite to that imparted to a flung ball, in addition to the juggler's mass, would exceed the bridge's tolerance (the bridge can tolerate a juggler and held ball, but not the additional downward force associated with forcing a ball 'up').
The correct answer is E because in order to juggle and have only 1 pin in his hand at a time he will have to impart a minimum accelerating force on that pin equivalent to the gravitational force of 4 pins. Lets assume 1 second in the hand with a constant acceleration for that second, plus 4 seconds in the air for each pin. Therefore to throw the pin and have it come back in 4 seconds you need to accelerate it at 4 x 9.8ms-1. This equals the same force as holding 4 pins in your hand with only the basic 9.8ms-1 acceleration of gravity on them, add the weight of the pin being thrown and you have the 5 pins weight accounted for.
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