How long does is remain in the air?

  • #1
I really don't understand my physics class... Can anyone help me on these questions?

1. A ball falls from rest from a height of 490m.
a. How long does is remain in the air?
b. If the ball has a horizontal veolcity of 200m/s when it begins to fall, what horizontal displacement will it have?

2. A bridge is 176.4m above a river. If a lead weighted fishing line is thrown from the bridge with a horizontal velocity of 22.0m/s, how far has it moved horizontally when it hits the water?
 

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  • #2
arildno
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Sure, could you post some of your thoughts/work on this?
In particular, what formulas do you think is appropriate here, or why are you unsure about their use?
 
  • #3
BobG
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SnitchSeekaHarry said:
2. A bridge is 176.4m above a river. If a lead weighted fishing line is thrown from the bridge with a horizontal velocity of 22.0m/s, how far has it moved horizontally when it hits the water?
Dang, that's one high bridge. What's he doing fishing off of that? (Royal Gorge would be worse - not only is it 320 m high, the distance it has moved horizontally is going to be pretty irrelevant when it hits the rapids down at the bottom of gorge. Better fish off the downstream side.)

But, yeah, you should at least toss out some ideas for us to make fun of (I mean, refine and assist you with). :rofl:
 
  • #4
I really don't have any idea, my physics teacher just gives out problems for homework, without even teaching. Can you anyone tell what topic these problems are covered on, that way I might get an idea.
 
  • #5
FredGarvin
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Look for the section that discusses equations of motion for a constant acceleration.
 
  • #6
dextercioby
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And Newton's second law...You'll need it right at the very beginning.

Daniel.
 
  • #7
arildno
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SnitchSeekaHarry said:
I really don't have any idea, my physics teacher just gives out problems for homework, without even teaching. Can you anyone tell what topic these problems are covered on, that way I might get an idea.
I'm sorry, I don't believe you.
He does actually open his mouth from time time, doesn't he?
But have you paid any attention to what he said, or at least read in your textbook occasionally?
 
  • #8
Actually, no one has an A in that class. Since he is also an AP teacher, he expects us to know, but we're only actually in honors. He just gives out these labs and problems, then after every week, we get a test.
 
  • #9
It's ok if no one can or wants to help coz they don't believe, it's just homework, he doesn't care about it anyway, all he cares about are the tests. I just wanted to understand for the next test.
 
  • #10
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Hint: what can you say about the initial and final conditions for the following properties:

position (relative to some defined coordinates)
velocity
acceleration
time

create a list of those values for the initial AND final conditions (anything you don't know put a ? ). You'll then need to solve for the unknowns using your kinematics equations
 
  • #11
Curious3141
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SnitchSeekaHarry said:
It's ok if no one can or wants to help coz they don't believe, it's just homework, he doesn't care about it anyway, all he cares about are the tests. I just wanted to understand for the next test.
OK, if your teacher is useless (your opinion) and you don't have a book, don't despair, the Internet can save you. Read this from start to end to get the basic knowledge you need. The third page after that link (press "NEXT") will teach you about free-fall problems, but I'd suggest you read it all. Take another crack at the problem after you've learnt something and post your working here. You have to take some effort before you get any help.
 
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  • #12
arildno
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SnitchSeekaHarry said:
It's ok if no one can or wants to help coz they don't believe, it's just homework, he doesn't care about it anyway, all he cares about are the tests. I just wanted to understand for the next test.
1) Do you know what "position" is, and how it is related to "acceleration"?
2) What does it mean when we say that the acceleration is constant?
3) Have you heard about Newton's laws of motion?

Do not even try to imply that you haven't even got a textbook where such stuff is described.
 
  • #13
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OK, first off, state for us Newton's Laws of Motion.

Second, look in your book for the chapter(s) on projectile motion. Copy down every equation in that chapter and post them here.

If by that point you still cannot figure out the problem (doing the above will give some some pretty BIG clues), then I am sure someone will give you more hints.

If we just gave it to you, you still wouldnt retain it for the test you speak of. You need to do it. Only way to learn....
 

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