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posted by  Jim Paulin on 11/3/2009 10:07:18 PM  |  status: Closed  |  Earned Karma: 368

projectiel motion

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N/A N/A N/A N/A 11/4/2009 at 7:00:00 AM
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How long will it tkae a shell fired from a cliff at an initial velocity of 800 m/s at an angle 30 degrees below the horizontal to reach the ground 150 meters below?  the answer is 0.37 seconds
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posted by esther_jyothi on 11/3/2009 10:10:56 PM  |  status: Live
Asker's Rating: Somewhat Helpful   
Response Details:
Given  
        Horizontal range  R  = 150 m 
                   initial velocity  u  = 800 m/s 
                    angle     θ       =  30 deg 
            we know that    R  = ( u sin θ  )  t 
                                  t   = R  /  u sin θ 
                                        = 150  / 800 x sin 30 
                                         =   0.375 sec
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posted by Jim Paulin on 11/3/2009 10:15:08 PM  |  status: Live
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Response Details:
but the horizontal range is not 150 and  is not given, only the vertical distance of 150 meters is known, doesn't acceleration due to gravity have to factor in?
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posted by Marth on 11/3/2009 10:21:39 PM  |  status: Live
Asker's Rating: Lifesaver   
Response Details:
The initial velocity is found by .





Use the Quadratic Formula to solve.  




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"Lois Lane is falling, accelerating at an initial rate of 32ft per second per second. Superman swoops down to save her by reaching out two arms of steel. Ms. Lane, who is now traveling at approximately 120 miles per hour, hits them, and is immediately sliced into three equal pieces." - Sheldon
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posted by fnkyfrsh on 11/3/2009 10:39:42 PM  |  status: Live
Asker's Rating: Helpful   
Response Details:
since the vector here is going down and to the right you will need to use Vcosθ and -Vsinθ
set up the data table
= 800cos(30)  = -800sin(30) or -400m/s
= 800cos(30)   = ?
= ?                  = 0m
= 0m              = 150m       
 a =  0m/s^2            a =  -9.8m/s^2
 t = ?                       t = ?
using the y's
-800sin(30) = -400
= -400^2 + 2(-9.8)(-150)
=
 v = 403.66 but since it is in the down direction it is -403.66
now use
t=
t=
t
t=.37s
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