bii17
The base diameter and altitude of a right circulAR cone are observed at a certain instant to be 10 and 20 inches respectively. if the lateral area is constant and the base diameter is increasing at a rate of 1 inch per cubic minute, find the rate at ehich the altitude is decreasing
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bii17
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hmm yes.. he formula is LA = pi*r*L
Gowthaman
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1 inch per cubic minute .... means what ? i am not understanding ' CUBIC MINUTE'
bii17
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im sory it's 1 inch per minute
Gowthaman
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LA = pi*r*L , and here L is slant height
bii17
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yes...
Gowthaman
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|dw:1348992383404:dw|
bii17
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what happn nxt?
Gowthaman
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is it 1/ sqrt(2) inch/ min
bii17
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the answer will be 2.25 in per min @Gowthaman
Gowthaman
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then somewhere i missed, i check once again
bii17
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okay
Gowthaman
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but now i got -.25 inch/min
Gowthaman
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dh/dr =-1/2 (from condition of constant LS area) and dr/dt = 1/2 inch/min (given in the problem)
dh/dt = dh/dr x dr/dt = - 1/2 x 1/2 = - 1/4 = -0.25 inch / min
Gowthaman
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@bii17 ....?
sauravshakya
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|dw:1348995046484:dw||dw:1348995119250:dw||dw:1348995143495:dw|
sauravshakya
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|dw:1348995200114:dw|
sauravshakya
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I hope u can solve it from here...
bii17
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@sauravshakya hey stil there?
bii17
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|dw:1349001368987:dw|
bii17
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@sauravshakya what is that?? i didnt understand those with circle..
sauravshakya
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That is radius of the cone
sauravshakya
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Got it?
sauravshakya
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ALSO,|dw:1349001642850:dw|
bii17
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@hartnn can u help me in this question?
hartnn
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which part of saurav's explanation did u not understand?
bii17
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here.. |dw:1349002226151:dw| i used it but i didnt get the correct answer the answer should be 2.25 @hartnn
hartnn
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@bii17 i did get it as 2.25. l^2=425, r=5, h=20, dr/dt=2
bii17
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|dw:1349002789725:dw| i get is 8 @hartnn
hartnn
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oh sorry, dr/dt = 1/2 and not 2
bii17
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|dw:1349002976588:dw| my answer is 2.. :( @hartnn can u show me what u did?
hartnn
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|dw:1349002984911:dw|
hartnn
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did u get that u missed the -*minus* sign in the beginning ?