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posted by  paduama on 6/14/2008 9:21:43 PM  |  status: Live  

Need help with trajectory question, will rate lifesaver. TY

Course Textbook Chapter Problem
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Question Details:
Determine the time of flight and the range R of the trajectory
 
 
 
The answer should be:
t=2.5
R=19
 
I know how to find R, I'm just having trouble with t.
 
Thanks for the help

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posted by zsm28 on 6/14/2008 11:43:55 PM  |  status: Live
Asker's Rating: Helpful   
Response Details:

angle θ = 40 degrees
angle between AB and horizontal = φ, tanφ = 3/4

horizontal: R = vocosθ*t,          (1)

vertical: -Rtanφ = vosinθ *t - gt2/2         (2)

plug (1) into (2)

-vocosθtanφ*t = vosinθ *t - gt2/2  

divide it by t

-vocosθtanφ = vosinθ - gt/2 

∴t = 2vo(sinθ + cosθtanφ)/g = 2.5 s

plug it into (1)

R = 19 m
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posted by paduama on 6/15/2008 12:34:21 AM  |  status: Live
Asker's Rating: N/A-Posted by Person Asking Question   
Response Details:
Correct me if I'm wrong but,

t = 2vo(sinθ + cosθtanφ)/g

t=2(10)[sin40+cos40arctan(3/4)]/9.81

t does not equal 2.5
Oracle
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posted by zsm28 on 6/15/2008 1:39:00 AM  |  status: Live
Asker's Rating: Lifesaver   
paduama's comment:
"oh ok. thanks"
Response Details:
t = 2vo(sinθ + cosθtanφ)/g

t=2(10)[sin40+cos40arctan(3/4)]/9.81
here arctan should be deleted, note tanφ = 3/4
so
t=2(10)[sin40+cos40(3/4)]/9.81 = 2.481
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posted by paduama on 6/15/2008 10:49:05 AM  |  status: Live
Asker's Rating: N/A-Posted by Person Asking Question   
Response Details:
I dont understand why arctan is deleted, could someone please explain this to me.

Thank You
Sage
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posted by Mr.K A T T A on 6/16/2008 3:48:44 AM  |  status: Live
Asker's Rating: Helpful   
paduama's comment:
"thanks"
Response Details:
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