Answer:
105 minutes
Explanation:
The pond is a prism. Its volume is the area of the trapezoidal base (the front and back faces) multiplied by the height (the 1 m edge).
Area of base of pond (front face) = (1/2)(B + b)h
Base = (1/2)(1.5 m + 0.6 m)(2 m) [Here, height is the height oif the trapezoid, so it is 2 m]
Base = 2.1 m²
Volume = Base × Height
Volume = 2.1 m² × 1 m [Here, height is the height of the prism, so it is 1 m]
Volume = 2.1 m³
The volume of the upper 30 cm (= 0.3 m) of the pond is:
V = LWH
V = 2 m × 1 m × 0.3 m
V = 0.6 m³
The volume of water decreased 0.6 m³ in 30 minutes.
In 60 minutes, it would decrease by 1.2 m³.
60 minutes = 1 hour
The flow rate is 1.2 m³ / hour.
The total volume of the pond is 2.1 m³.
Emptying out the pond completely means removing 2.1 m³ of water at the flow rate of 1.2 m³/hour.
flow rate = volume/time
time × flow rate = volume
time = volume / flow rate
time = 2.1 m³ / 1.2 m³/hour = 1.75 hour
time = 1.75 hour × 60 minutes/hour = 105 minutes
Answer: 105 minutes