DP Physics (last assessment 2024)
Question 18M.2.SL.TZ2.5a.ii
| Date | May 2018 | Marks available | [Maximum mark: 3] | Reference code | 18M.2.SL.TZ2.5a.ii |
| Level | SL | Paper | 2 | Time zone | TZ2 |
| Command term | Show that | Question number | a.ii | Adapted from | N/A |
a.ii.
[Maximum mark: 3]
18M.2.SL.TZ2.5a.ii
In a pumped storage hydroelectric system, water is stored in a dam of depth 34 m.
The water leaving the upper lake descends a vertical distance of 110 m and turns the turbine of a generator before exiting into the lower lake.
Water flows out of the upper lake at a rate of 1.2 × 105 m3 per minute. The density of water is 1.0 × 103 kg m–3.
(a.ii)
Show that the average rate at which the gravitational potential energy of the water decreases is 2.5 GW.
[3]
Markscheme
mass per second leaving dam is × 103 = «2.0 × 106 kg s–1»
rate of decrease of GPE is = 2.0 × 106 × 9.81 × 127
= 2.49 × 109 «W» /2.49 «GW»
Do not award ECF for the use of 110 m or 144 m
Allow 2.4 GW if rounded value used from (a)(i) or 2.6 GW if g = 10 is used
[3 marks]
