Desmond builds a set of towers out of blocks. The table shows the number of blocks in each tower. Tower # 1 2 3 4 5 Number of bl
1 answer:
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The magnitude of the friction force is 25 N
Explanation:
To solve this problem, we just have to analyze the forces acting on the block along the horizontal direction. We have:
- The horizontal component of the pulling force,
, where F = 50 N is the magnitude and
is the angle between the direction of the force and the horizontal; this force acts in the forward direction
- The force of friction,
, acting in the backward direction
According to Newton's second law, the net force acting on the block in the horizontal direction must be equal to the product between the mass of the block and its acceleration:
where
m is the mass of the block
is the horizontal acceleration
However, the block is moving at constant speed, so the acceleration is zero:
So the equation becomes
(1)
The net force here is given by
(2)
And so, by combining (1) and (2), we find the magnitude of the friction force:
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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.
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