IB Physics SL A.3.10 Gravitational Potential Energy Question Bank

Practise calculating gravitational potential energy from mass, weight and height, including specific energy and energy rates.

Exam points

Calculate gravitational potential-energy change from mass, weight and vertical height, keeping units consistent.
Use specific energy or energy rate per kilogram to analyse water storage, tides and powered hill climbs.
Relate gravitational potential-energy changes to work, friction, speed or useful electrical output.

[Maximum number: 3]

This question is about a tidal power station.

A tidal power station is built for a coastal town. Sea water is stored in a tidal basin behind a dam at high tide and released in a controlled manner between high tides, so that it passes through turbines to generate electricity.

The following data are available.

Table for Question A.3.10—Gravitational potential energy question 1 — IB Physics SL

Calculate the electrical energy produced between successive high and low tides.

difference in height of centre of mass of water $=\frac{1.8}{2}=0.9(\mathrm{~m})$ ;
$\Delta E_{\mathrm{P}}\left(=m g \Delta h=2.8 \times 10^{8} \times 9.8 \times 0.9\right)=2.5 \times 10^{9}(\mathrm{~J}) ;$
electrical energy $\left(=0.24 \times 2.5 \times 10^{9}\right)=5.9 \times 10^{8}(\mathrm{~J})(=590 \mathrm{MJ})$ ;

Marking guidance:

Allow ECF for [2 max] if candidate omits factor of 2 in first marking points.
Accept $g=10 \mathrm{~m} \mathrm{~s}^{-2}$ giving an answer of $6.0 \times 10^{8}(\mathrm{~J})$ .

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A.3.10—Gravitational potential energy question 1