shows a mixing tank initially containing 2000 lb of liquid water. The tank is fitted with two inlet pipes, one delivering hot water at a mass flow rate of .8 lb/s and the other delivering cold water at a mass flow rate of 1.2 lb/s. Water exits through a single exit pipe at a mass flow rate of 2.5 lb/s. Determine the amount of water, in lb, in the tank after one hour

the water that remain in the tank in one hour will be 200 lb

Explanation:

Initial mass of water in the tank = 2000 lb

hot water is delivered through the first inlet pipe at a rate of = 0.8 lb/s

cold water is delivered through the second inlet pipe at a rate of = 1.2 lb/s

exit pipe flow rate = 2.5 lb/s

amount of water in the tank after one hour = ?

In one hour, there are 60 x 60 seconds = 3600 sec, therefore

the water through the first inlet pipe in one hour = 0.8 x 3600 = 2880 lb

the water through the second inlet pipe in one hour = 1.2 x 3600 = 4320 lb

the water through the exit in one hour = 2.5 x 3600 = 9000 lb

The total amount of water in the tank = 2000 + 2880 + 4320 = 9200 lb

The total amount of water that leaves the tank = 9000 lb

therefore, in one hour, the water that remain in the tank will be

==> 9200 lb - 9000 lb = 200 lb

the entire statement is true and correct.  

there's no diagram, nothing is illustrated, and no question is asked.

the answer is b, have negligible mass