The UK uses renewable energy resources to generate some of its electricity - AQA - GCSE Physics - Question 4 - 2023 - Paper 1

To calculate the gravitational potential energy (Ep) of the water, we use the formula:

$E_p = ext{mass} imes ext{gravitational field strength} imes ext{height}$

Substituting in the values:

$E_p = 2{,}500{,}000 ext{ kg} imes 9.8 ext{ N/kg} imes 15.0 ext{ m}$

Calculating this gives:

$E_p = 367{,}500{,}000 ext{ J}$

The equation linking energy, power, and time is:

$E = P imes t$

First, convert 60 minutes to seconds:

$t = 60 ext{ min} imes 60 ext{ s/min} = 3600 ext{ s}$

Using the equation:

$E = P imes t$

Substituting the values:

$E = 3000 ext{ W} imes 3600 ext{ s}$

Calculating this gives:

$E = 10{,}800{,}000 ext{ J}$

One reason why the power output varied is that the level of the water in the river changes, which can be affected by seasonal variations in rainfall and can be lower during the summer months.