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January 17th, 2008, 01:59 PM  #1 
Newbie Joined: Jan 2008 Posts: 2 Thanks: 0  Related Rates Problem Please Help!!!
Can anyone help me out with these questions? I'm so lost in this unit... lol I have 3 questions left and I really need help on them. Water runs into a tank that is in the shape of an inverted cone at the rate of 9cubic feet/min. The tank has a height of 10 ft and a base radius of 5 ft. How fast is the water level rising when the water is 4 ft deep? The length of the base of a right triangle is increasing at the rate of 12in/min. At the same time, the height of the triangle is decreasing in such a way that the length of the hypotenuse remains 10 inches. How quickly is the height of the triangle changing when the length of the base is 6 inches? A spherical balloon is being inflated so that its volume is increasing at the rate of 5 cubic meters/min. At what rate is the diameter increasing when the diameter is 12m? (V = 4/3(pi)r^3) Thanks in advance! 
January 17th, 2008, 02:24 PM  #2 
Newbie Joined: Jan 2008 Posts: 1 Thanks: 0 
Dude it doesn't help you if I just give you the answer. I will give you a hint For the 1st question use similar triangles. For the 2nd use pythagorem theorm then take the derivitive respect to dt. dx/dt would be 12in/min . You have the formula for the last one you probably need to write equation interms of d.. subsitute d/2=r. (pi(d)^2)/2(dd/dt)=dv/dt substitute dv/dt= 5m^3/min then solve for dd/dt

January 17th, 2008, 05:29 PM  #3 
Newbie Joined: Jan 2008 Posts: 2 Thanks: 0 
ok nvm i think i got the answers could u double check please? In order 1) 9/4(pi) 2) 3/4 3) 5(pi) / 72 
January 18th, 2008, 04:57 AM  #4 
Global Moderator Joined: Dec 2006 Posts: 18,595 Thanks: 1492 
You've made some errors; please post you're working.


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