BrainDen.com - Brain Teasers

# Izzy

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1. ## Two Dimensional Motion Using Vectors

I missed much of my physics lecture on Friday, so I'm not entirely sure what I'm doing, and we have a homework quiz on this Monday. =/ If this seems really trivial.. it probably is, but I wasn't there to learn it (so don't judge me >_>). The homework is pretty much all reminiscent of this problem, so if I understand this, I should be clear. Check mah answerz pwease? A river flows due east at 1.50 m/s. A boat crosses the river from the south bank to the north bank by maintaining a constant velocity of 10.0 m/s due north relative to the water. a. What is the velocity of the boat as viewed by an observer on the south bank? b. If the river is 325 m wide, how much time will it take for the boat to cross the river? c. How far downstream is the boat when it reaches the north bank? d. What is the boat's displacement? e. What is the magnitude of the boat's displacement? f. What is the boat's average speed? My answers, work omitted. a. 10.1 m/s NE b. 32.2 seconds c. 12.0 m d. 325.22 m NE e. 325.22 m at 87.8° North of East f. 10.1 m/s
2. ## Green and Yellow hats again, but harder

So, same solution as above (the upvoted post if you can't see it chronologically), but the "people in front of them" are the people that get taken aside before them?
3. ## I’m not a gardener

It kind of makes me think of

7. ## Random triangles in a circle

Found the mistake!
8. ## Green and Yellow hats

@bonanova Just calculated the groups of three case, and half the time two people are saved, and the other half one person is saved. So, you get the same expected value, but can't guarantee as many.

10. ## Random triangles in a circle

@Molly Mae, that doesn't quite work. You can draw some counter examples. It did give me a good idea, though.
11. ## Green and Yellow hats

@bonanova, it should be the second post in the thread. Someone upvoted it, so it's no longer in chronological order. Thanks. Honestly, I was going to keep trying to come up with a better one, so thanks for putting me out of my misery. Is there a way to prove that there isn't a *better* solution?

13. ## Green and Yellow hats

@Molly Mae, here is a demonstration that the answer can bestrictly greater than zero.

15. ## Green and Yellow hats

@bonanova, is the warden perfectly logical? Are the prisoners perfectly logical?

17. ## Green and Yellow hats

Are they allowed to move at all, like to sort themselves without communication? Or do they start off in their positions in the room with hats placed on them, only allowed to say one word?

24. ## Born on a Wednesday

Let's see if I remember some probability.
25. ## Good-natured Trump jokes

A joke from the internet yesterday: Trump really delivered when he said he would run the government just like his businesses. It's already shutdown! Don't worry, he still has three years to bankrupt it.
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