4. In a closed system consisting of a cannon and a cannonball, the kinetic energy of a cannon is 72,000 J. If the cannonball is
2 answers:
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a) Potential difference needed: 10,000 V
b) Because the potential difference in the house is maximum 230 V
Explanation:
a)
The relationship between current, potential difference and resistance in a conductor is given by Ohm's law:
where
V is the potential difference
R is the resistance
I is the current
The resistance of the human body is estimated to be as high as for a dry body and as low as
for a wet body: in this problem, we use a value in the middle,
Therefore, the potential difference needed to produce a current of
is
b)
Here we want to estimate if it is likely or not to get injured by an electric current in a house.
The amount of current that can be fatal is . From part a), we saw that in order to produce this current through the human body, a potential difference of
is needed.
However, the electricity that reaches the houses and then is connected to the household appliances has a potential difference of
V = 230 V
This value is much lower than 10,000 V, therefore the electricity in the house is unlikely to cause injures to human body.
Learn more about potential difference:
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