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Brain Teaser! September 5, 2009

posted by RK -Cramster US on 9/5/2009 12:52:18 PM

Here is this week's brain teaser. Remember to post your answer to the discussions tab of the Cramster.com Facebook Fan Page!

Here's the latest brain teaser:

A circus juggler must perform a trick in which he crosses a narrow bridge juggling three balls. He weighs 80 kg and each one of the balls weighs 10 kg.

The bridge can only hold 100 kg before collapsing. The lion tamer said that as long as he kept one ball in the air, the bridge won't collapse. Is this true?

Know the answer?

First one to post the correct answer to the discussion tab of the Cramster.com Facebook Fan Page gets 10 karma points this week!

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COMMENTS:

posted by kirkulator on 9/24/2009 6:59:12 PM HAHAHAH.when you stand on a bridge, the only force youre exerting onto it is your own weight [mass x gravity], but when you throw somthing upward and it falls back down onto that bridge, the force that falls back down is greater [mass x its acceleration] it may hold 100kg but add a little downward force and it is like adding weight....the lion tamer is wrong.
posted by bk12321 on 9/22/2009 10:15:26 AM No the lion tamer is wrong because of the balls' momentum, and because of the downward force created when the juggler throws the ball back up. When the balls come down, their momentum will be great enough that it will 'appear' like they are actually heavier than 10 pounds when he catches them. Its kind of like the elevator effect, where when you are going down in an elevator you feel lighter, but if it abruptly stops you feel much heavier for a split second because of your momentum. Your weight will actually increase in that split second, as will your force on the elevator floor. Same in this instance.
posted by Anonymous on 9/19/2009 7:23:06 PM The lion tamer is wrong because at the time he push one of the balls to the air he is pushing himself down to the earth gaining some more wight for an instant,if at that instant he is holding two more balls the result is more than 100 pounds.
posted by Anonymous on 9/16/2009 11:19:14 PM i think lion is wrong.. weight goes to 100 + as he catches the ball because of gravity of ball
posted by DanlB on 9/11/2009 6:36:26 PM He tosses the first ball so it is in the air as he steps on the bridge. The total mass on the bridge is now 100 kg. When he catches the ball the mass on the bridge increases to 100 kg plus an impulse term (80 kg for the man, 20 kg for the two balls he was holding and 10 kg (plus an that impulse term) for the ball he just caught. To make a long story short the bridge breaks. However, if he tosses a second ball at exactly the same time he catches the first ball some of the "mass" of the first ball coming down is cancelled by the "mass" of the second ball going up. However there is still the impulse term to consider. Both the ball being thrown up and the ball coming down will cause an impulse to be applied to the man and hence the bridge so I say the bridge will break with just one ball in the air. But in this case, one ball isn't always in the air as the two balls are in contact with the jugglers hands at the same time. But, if he tosses the first ball, tosses the second ball then steps on the bridge, catches the first ball at exactly the same time he tosses the third ball, catches the second ball at exactly the same time he drops the first ball etc, the juggler has a small safety margin and it could “in theory” be done. Because the juggler is catching and dropping two balls at the same time, one could say only one ball is totally in free flight (in the air at all times). Too much brain strain for me to do the math.
posted by Anonymous on 9/10/2009 11:55:40 PM i guess its true. it is because when the ball falls freely, it experiences no weight at all. so
posted by MrBullwinkle on 9/10/2009 11:00:05 PM If he kept 2 balls in the air, then it leaves room for him to accelerate the ball in hand upward with F=g*m without exceeding the "mass". However, as the lion tamer has stated with only 1 ball in the air, there is no room for upward acceleration without applying too much force to the bridge.
posted by Jordan Rey on 9/9/2009 3:14:37 PM No. The clown exerts a force on the third ball in throwing it up, and from Newton's laws, there is an equal/opposite reaction every time he throws the balls. Since he is juggling three balls, and is throwing them against gravity (meaning he is accelerating the ball at a greater magnitude than 9.81 m/s^2), the combined force transferred to the bridge will more than likely be more than 20kg*9.81, therefore, the combined weight will be more than 981 N, which is the max. the bridge can handle assuming no factor of safety is included in that number.
posted by GeorgeB on 9/7/2009 8:39:50 PM They clown will break the bridge. Since 100kg is not a weight, rather a mass, the clown will be exerting an equivalent force to holding three balls due to the force used to toss the ball in the air reacting against it. The equivalent force/weight of all three balls will always be acting upon the clown.
posted by Tulaib on 9/7/2009 7:32:45 AM it is true...no ambiguities in it
posted by Pretty Sam on 9/6/2009 10:51:36 PM Yes, because 80+10+10=100 so as longas 1 ball is in the air he wont weigh 110 which will make the bridge fall.
posted by Anonymous on 9/6/2009 8:35:59 PM It seems kinda true. But since it is a brain teaser. NO!!!!!! 1. In the process of throwing the ball up he gives the bridge additional forces in the vertical causing it to collapse and also the ball may have additional force in coming down.

posted by kirkulator on 9/24/2009 6:59:12 PM

HAHAHAH.when you stand on a bridge, the only force youre exerting onto it is your own weight [mass x gravity], but when you throw somthing upward and it falls back down onto that bridge, the force that falls back down is greater [mass x its acceleration] it may hold 100kg but add a little downward force and it is like adding weight....the lion tamer is wrong.

posted by bk12321 on 9/22/2009 10:15:26 AM

No the lion tamer is wrong because of the balls' momentum, and because of the downward force created when the juggler throws the ball back up. When the balls come down, their momentum will be great enough that it will 'appear' like they are actually heavier than 10 pounds when he catches them. Its kind of like the elevator effect, where when you are going down in an elevator you feel lighter, but if it abruptly stops you feel much heavier for a split second because of your momentum. Your weight will actually increase in that split second, as will your force on the elevator floor. Same in this instance.

posted by Anonymous on 9/19/2009 7:23:06 PM

The lion tamer is wrong because at the time he push one of the balls to the air he is pushing himself down to the earth gaining some more wight for an instant,if at that instant he is holding two more balls the result is more than 100 pounds.

posted by Anonymous on 9/16/2009 11:19:14 PM

i think lion is wrong.. weight goes to 100 + as he catches the ball because of gravity of ball

posted by DanlB on 9/11/2009 6:36:26 PM

He tosses the first ball so it is in the air as he steps on the bridge.

The total mass on the bridge is now 100 kg.

When he catches the ball the mass on the bridge increases to 100 kg plus an impulse term (80 kg for the man, 20 kg for the two balls he was holding and 10 kg (plus an that impulse term) for the ball he just caught. To make a long story short the bridge breaks.

However, if he tosses a second ball at exactly the same time he catches the first ball some of the "mass" of the first ball coming down is cancelled by the "mass" of the second ball going up. However there is still the impulse term to consider. Both the ball being thrown up and the ball coming down will cause an impulse to be applied to the man and hence the bridge so I say the bridge will break with just one ball in the air. But in this case, one ball isn't always in the air as the two balls are in contact with the jugglers hands at the same time.

But, if he tosses the first ball, tosses the second ball then steps on the bridge, catches the first ball at exactly the same time he tosses the third ball, catches the second ball at exactly the same time he drops the first ball etc, the juggler has a small safety margin and it could “in theory” be done. Because the juggler is catching and dropping two balls at the same time, one could say only one ball is totally in free flight (in the air at all times).

Too much brain strain for me to do the math.

posted by Anonymous on 9/10/2009 11:55:40 PM

i guess its true. it is because when the ball falls freely, it experiences no weight at all. so

posted by MrBullwinkle on 9/10/2009 11:00:05 PM

If he kept 2 balls in the air, then it leaves room for him to accelerate the ball in hand upward with F=g*m without exceeding the "mass". However, as the lion tamer has stated with only 1 ball in the air, there is no room for upward acceleration without applying too much force to the bridge.

posted by Jordan Rey on 9/9/2009 3:14:37 PM

No. The clown exerts a force on the third ball in throwing it up, and from Newton's laws, there is an equal/opposite reaction every time he throws the balls. Since he is juggling three balls, and is throwing them against gravity (meaning he is accelerating the ball at a greater magnitude than 9.81 m/s^2), the combined force transferred to the bridge will more than likely be more than 20kg*9.81, therefore, the combined weight will be more than 981 N, which is the max. the bridge can handle assuming no factor of safety is included in that number.

posted by GeorgeB on 9/7/2009 8:39:50 PM

They clown will break the bridge. Since 100kg is not a weight, rather a mass, the clown will be exerting an equivalent force to holding three balls due to the force used to toss the ball in the air reacting against it.

The equivalent force/weight of all three balls will always be acting upon the clown.

posted by Tulaib on 9/7/2009 7:32:45 AM

it is true...no ambiguities in it

posted by Pretty Sam on 9/6/2009 10:51:36 PM

Yes, because 80+10+10=100 so as longas 1 ball is in the air he wont weigh 110 which will make the bridge fall.

posted by Anonymous on 9/6/2009 8:35:59 PM

It seems kinda true. But since it is a brain teaser. NO!!!!!!

1. In the process of throwing the ball up he gives the bridge additional forces in the vertical causing it to collapse and also the ball may have additional force in coming down.

Brain Teaser! September 5, 2009

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