I don't understand when to use the formule with the constant k, and when to use the formula without it.

Physics

1 answer:

White raven [17]2 years ago

3 0

Answer:

This appears to be the formula for the electrical force between 2 objects.

You need this constant to calculate the electrical force between 2 charged objects.

Note that k = (1 / 4 * π ∈0)

∈0 is called the permittivity constant and ∈0 = 8.85E-12 farad/m

k = ( 1 / (4 * 3.28 * 8.85E-12) = 8.99E9

This makes F reasonably easy to remember as

F = 9E9 Q1 * Q2 / R^2 Newtons for the electrical force between Q! and Q2 separated by R

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See the answers below.

Explanation:

In order to solve this problem we must use the principle of energy conservation. Which tells us that the energy of a body will always be the same regardless of where it is located. For this case we have two points, point A and point B. Point A is located at the top at 120 [m] and point B is in the middle of the cliff at 60 [m].

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$E_{B}=m*g*h+\frac{1}{2}*m*v^{2}$

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$(6.5*9.81*120)+(0.5*6.5*18^{2} )=(6.5*9.81*60)+(0.5*6.5*v_{B}^{2} )\\3.25*v_{B}^{2} =4878.9\\v_{B}=\sqrt{1501.2}\\v_{B}=38.75[m/s]$

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In order to calculate the velocity at the bottom of the cliff where the reference level of potential energy (potential energy equal to zero) is located, we must pose the same equation, with the exception that at the new point there is only kinetic energy.

$E_{A}=E_{C}\\6.5*9.81*120+(0.5*9.81*18^{2} )=0.5*6.5*v_{C}^{2} \\v_{c}^{2} =\sqrt{2843.39}\\v_{c}=53.32[m/s]$