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Water is running into a conical vessel, 18cm deep and 6cm in radius, at the rate of 0.1 cm3cm^3/sec. If the water is 4cm deep, then the water level rising at the rate

Solution

✅ Correct Option: 2

Similar triangles give rh=618\frac{r}{h}=\frac{6}{18}, so r=h3r=\frac{h}{3} and V=13πr2h=πh327V=\frac{1}{3}\pi r^2 h=\frac{\pi h^3}{27}. Then dVdt=πh29dhdt\frac{dV}{dt}=\frac{\pi h^2}{9}\frac{dh}{dt}. At h=4h=4 with dVdt=0.1\frac{dV}{dt}=0.1: dhdt=0.916π=9160π\frac{dh}{dt}=\frac{0.9}{16\pi}=\frac{9}{160\pi} cm/sec.

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