An empty bathtub has its drain closed and is being filled with water from the faucet at a rate of 10 kg/min. After 10 minutes the drain is opened and 4 kg/min flows out and at the same time the inlet flow is reduced to 2 kg/min. Plot the mass of the water in the bathtub versus time and determine the time from the very beginning when the tub will be empty.
During the first 10 minutes we have
dmcv/dt = mi = 10 kg/min ,
∆m = m . ∆t1 = 10 × 10 = 100 kg
So we end up with 100 kg after 10 min. For the remaining ** we have
