- #1

Clara Chung

- 304

- 14

## Homework Statement

A hydroelectric power plant is built next to a reservoir with a water turbine beneath a dam. In normal operation, which of the following conditions will increase the flow rate of water, in kg s^-1 ,through the turbine.

(1) There are too much water in the reservoir.

(2) After a heavy rainfall

(3) There is an increase in the demand of electricity

A. (1) only

B. (3) only

C. (1) and (2) only

D. (2) and (3) only

## Homework Equations

The answer is B.

flow rate = p A v

Power output max = p A v g h

where p is the density of water, A is the cross sectional area of the turbine, v is the speed of water.

## The Attempt at a Solution

I know that (1) is incorrect because the gates will be opened to release the excessive water.

(3) is correct because the inlet to the turbine will be widened. flow rate = p A v, p and A are unchanged, so the velocity of water increases to increase the flow rate.

However how should I explain (2), from my intuition the pressure difference increases because there is a higher water pressure due to pgh , speed of the water should increases which results in a larger flow rate, why is the flow rate unchanged?