9) At a construction site, a small crane is raising two boxes of nails on a plank to the roof. One box has already been opened a
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Answer:
Explanation:
In order to solve this problem we need to make a free body diagram of the book and the forces that interact on it. In the picture below you can see the free body diagram with these forces.
The person holding the book is compressing it with his hands, thus exerting a couple of forces of equal magnitude and opposite direction with value F.
Now the key to solving this problem is to analyze the equilibrium condition (Newton's third law) on the x & y axes.
To find the weight of the book we simply multiply the mass of the book by gravity.
W = m*g
W = 1.3[kg] * 9.81[m/s^2]
W = 12.75 [N]
The energy stored by a system of capacitors is given by
where Ceq is the equivalent capacitance of the system, and V is the voltage applied.
In the formula, we can see there is a direct proportionality between U and C. This means that if we want to increase the energy stored by 4 times, we have to increase C by 4 times, if we keep the same voltage.
Calling
the capacitance of the original capacitor, we can solve the problem by asking that, adding a new capacitor with 
, the new equivalent capacitance of the system 
must be equal to 
. If we add the new capacitance X in parallel, the equivalent capacitance of the new system is the sum of the two capacitance
and since Ceq must be equal to 4 C1, we can write
from which we find
where Ceq is the equivalent capacitance of the system, and V is the voltage applied.
In the formula, we can see there is a direct proportionality between U and C. This means that if we want to increase the energy stored by 4 times, we have to increase C by 4 times, if we keep the same voltage.
Calling
and since Ceq must be equal to 4 C1, we can write
from which we find