A tank in the shape of a right circular cone is full of water. The tank is 6ft. across the top and 8 ft. high. How much work is done in pumping water over the top edge.
(a) Set up the integral
(b) Solve using the graphing calculator.
I only need help with part (a). My professor gave the answer in class but I can't seem to get my answers to match. Her answer is: 4929
$$Water: 62.4 lb/ft^3$$
$$Radius: 3ft$$
$$Height: 8ft$$
$$\frac38 = \frac xy => x=\frac38y$$
$$w = \int_0^8 \pi x^2 dy (62.4)(8-y)$$
$$w = 62.4 \pi \int_0^8 \left({\frac38y} \right)^2(8-y)dy$$
Then I plug that into calculator. My answer is 1323.2 Which is wrong. I know my integral isn't set up correctly. So if you can help me out.
Best Answer
I cannot get the specified answer also. My way of interpret it is:-
(1) Set up a representative disc as shown. It should be clear that its volume is $πx^2(dy)$.
(2) At that instant, $x = (3/8)y$.
(3) To empty all the water out, integrate $\int_0^8 πx^2(dy)$.
(4) Work done = 62.4 times the result of (3) and I got 4705.
Note:- If work done is equal to rate times amount of water, then it is equal to $62.4 [(1/3) π 3^2 (8)]$ directly.