motion in two dimension

Discussion in 'Homework Help' started by fan_boy17, Apr 17, 2012.

1. fan_boy17 Thread Starter New Member

Apr 17, 2012
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a snowball rolls off a barn roof that slopes downwards at an angle of 40 degrees. the edge of the roof is 14m above the ground and the snowball has a speed of 7ms-1 as it rolls off the roof
(a) how far from the edge of the barn does the snowball strike the ground if it doesnt strike anything else.

cant seem to get the answer which is 6.93m :\

2. steveb Senior Member

Jul 3, 2008
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You have to show some effort before we can help you. What equations do you know for solving this type of problem?

Also, we need to know your background. This problem is trivial if calculus is applied, but if you don't know how to use calculus, we'll take another approach.

3. panic mode Senior Member

Oct 10, 2011
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HINT:
do the decomposition in x and y. note that there is no acceleration in x but there is acceleration in y (due gravity).

4. russ_hensel Well-Known Member

Jan 11, 2009
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Note that there is some extraneous data in the problem, and that you probably intended to approximate the diameter of the snowball as 0.

5. steveb Senior Member

Jul 3, 2008
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I don't see any extraneous data, but I agree there are some unspoken assumptions that are implied.

6. panic mode Senior Member

Oct 10, 2011
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i think he's gone...

assuming positive direction in X axis is away from barn wall, positive direction in Y axis is up and 40deg is measured from horizontal, since roof is sloping down this is actually -40deg:

Vo=7m/s
g=-9.8m/s
.....
X=...=6.93m

Last edited: Apr 18, 2012
7. steveb Senior Member

Jul 3, 2008
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You are not supposed to solve homework problems for the OP.

Why did you do this against the terms of service agreement?

Oct 10, 2011
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9. steveb Senior Member

Jul 3, 2008
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If you are not aware of our policy to not encourage abuse of our help, it's OK. That's why I pointed it out.

You are correct that it is not in the terms of service, nor in the replying to post sections. I just assumed it was, going from (faulty) memory remembering back to when I joined. Instead let's refer to the guidelines for posting homework which the OP must obey, as follows.

"When posting a request for homework/coursework/assignment help, you must provide details of your attempts at the questions. Any thread that just posts up a copy of the questions without any attempts on the part of the opening poster will be directed to this thread and will be given 48 hours to satisfy the requirements detailed within."

Also, please note my first comment in this thread.

"You have to show some effort before we can help you. What equations do you know for solving this type of problem?"

Here I'm notifying the OP of his requirement to follow the guidelines. When one member does this, other members should wait for a response. As you say, he is probably not coming back. He either figured it out himself, or is lurking as an anonymous user hoping one of us will violate our own policies. I don't think we should encourage cheating. We used to see this happen, and then once the person got the answer, he would delete the original question and run. Bill has since prevented this by limiting the ability of new users to delete posts.

10. Wendy Moderator

Mar 24, 2008
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Problem is, this is not the homework thread. It probably should be moved, whatcha think?

11. steveb Senior Member

Jul 3, 2008
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I think that is a moderator's call whether to move it, but it is a homework thread wherever it lies. Hence it should be treated the same in either place. Otherwise, students will exploit the loophole in the system.

Anyway, this is my final straw as far as helping new users with homework. I'll help established users with a track record for coming back and interacting properly. I've even noted some regular users that have deleted some of their questions after getting answers. As I find them, they go on to my ignore list.

12. russ_hensel Well-Known Member

Jan 11, 2009
818
47

Actually I think you are right, I was a bit to hasty. Actually I think all but the simplest problems are improved by extraneous data, more like real life.

13. steveb Senior Member

Jul 3, 2008
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I agree completely. Too many problems corral the student into a path to the solution with the data given in a perfect form. Real world problem solving is much more difficult.

Last edited: Apr 19, 2012
14. WBahn Moderator

Mar 31, 2012
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I promise that if anyone ever answers the question I asked in my very first post to the forum that I will not delete it! Promise! ;-)