Can someone please help me on this question and explain how to get the answer?
You may find the following formula and information useful when answering some parts of this question.
Change in gravitational potential energy = weight _ change in vertical height
(joule, J) (newton, N) (metre, m)
On Earth, 1 litre of water weighs 10 N.
A hydroelectric power station uses two lakes, A and B.
10.1 When 6 litres of water fall from lake A to lake B, 1500 J are transferred.
How far has the water fallen?
A 2.5m
B 25.0m
C 250.0m
D 2500.0m
10.2 If the input power to the turbine is 1.5kW, how long has it taken for the water to fall?
A 0.1 s
B 1.0 s
C 10.0 s
D 100.0 s
10.3 Another hydroelectric power station allows water to fall 20 m to the turbine.
Only 20% of the gravitational potential energy lost is transferred into electricity.
How many litres of water must fall in order to generate 4 kWh of electricity?
A 6000
B 72 000
C 360 000
D 3 600 000
x
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- 28-06-2004 16:53
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- 28-06-2004 17:43
anyone?
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- 28-06-2004 18:07
B
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A -
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- 28-06-2004 18:08
Keep thinking about definitions of power and the equation they give you.
Write it out and plug in the information you are given.
Then try to work out what they want.
and watch out for unit changes kW--> 1000W, hr--> 60secs, that sort of thing.
A hydroelectric power station uses two lakes, A and B.
10.1 When 6 litres of water fall from lake A to lake B, 1500 J are transferred.
How far has the water fallen?
A 2.5m
B 25.0m
C 250.0m
D 2500.0m
using the equation ^GPE=weight^h (^ as delta/change in)
1500 = 60*h
h = 1500/60 = 25.0m (B)
10.2 If the input power to the turbine is 1.5kW, how long has it taken for the water to fall?
A 0.1 s
B 1.0 s
C 10.0 s
D 100.0 s
since 1.5kW = 1500 W
1500 = 1500/t
t = 1500/1500 = 1.0s (B)
10.3 Another hydroelectric power station allows water to fall 20 m to the turbine.
Only 20% of the gravitational potential energy lost is transferred into electricity.
How many litres of water must fall in order to generate 4 kWh of electricity?
A 6000
B 72 000
C 360 000
D 3 600 000
E = 4kW*60s = 4000*60 = 240000J
only 20% efficient, so work done by water is
240000/20% = 1200000J
Since ^GPE=weight^h
1200000 = (weight of water)*20
weight of water = 1200000/20 = 60000N
Since "On Earth, 1 litre of water weighs 10 N."
weight of water = 60000N = 10*n (n being number of litres)
n = 60000/10 = 6000litres
-----------------------
Is that ok?
selkie -
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- 28-06-2004 18:11
(Original post by selkie222)
Is that ok?
selkie
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Updated: June 28, 2004
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