Solve this:
Water is poured into inverted conical vessel of which the radius of the base is 2m and height 4m, at the rate of 77 liter/minute. The rate at which the water level is rising at the instant when the depth is 70 cm is:(use  π  = 22/7).
(1) 10 cm/min           (2) 20 cm/min           (3) 40 cm/min           (4) none        

Here for cone r = 2 m = 200 cmh = 4 m = 400 cm and dVdt= 77 litre/minute = 77000 cm3/minuteV = 13πr2hhere r = h2sp V= πh3×h24=πh312differentiate wrt t dVdt= π12×ddth3= 3πh212dhdt 77000= πh24×dhdtNow wen h is 70 cm then dhdt=77000×4×722×70×70=20 cm/minute

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