Q3.
The data is given so that candidate can find the Lv with rate of heat loss being taken into account.
The formula is:
P = mLv + H where m is rate of mass evaporated and H = rate of heat loss
when power is altered , the rate of mass loss will be too but not H (rate of heat loss) (1) - (2) becomes P1-P2 = (m1-m2) Lv, Lv can be calculated with H already taken into account.
Q4.
When the sun shine on the water the power at which heat falls on it can be calculate by mulitiplying Ixarea. The rate of heat absorbed P = mL, where m is the rate of mass loss due to evaporation. Volume rate = mass rate / density. The flow rate from the reservior is the flow rate to town + rate of volume loss to evaporation. Hence adding this two terms will give rate of water supplied by reservior .
