Respuesta :
A) The work done by the electric field is zero
B) The work done by the electric field is [tex]9.1\cdot 10^{-4} J[/tex]
C) The work done by the electric field is [tex]-2.4\cdot 10^{-3} J[/tex]
Explanation:
A)
The electric field applies a force on the charged particle: the direction of the force is the same as that of the electric field (for a positive charge).
The work done by a force is given by the equation
[tex]W=Fd cos \theta[/tex]
where
F is the magnitude of the force
d is the displacement of the particle
[tex]\theta[/tex] is the angle between the direction of the force and the direction of the displacement
In this problem, we have:
- The force is directed vertically upward (because the field is directed vertically upward)
- The charge moves to the right, so its displacement is to the right
This means that force and displacement are perpendicular to each other, so
[tex]\theta=90^{\circ}[/tex]
and [tex]cos 90^{\circ}=0[/tex]: therefore, the work done on the charge by the electric field is zero.
B)
In this case, the charge move upward (same direction as the electric field), so
[tex]\theta=0^{\circ}[/tex]
and
[tex]cos 0^{\circ}=1[/tex]
Therefore, the work done by the electric force is
[tex]W=Fd[/tex]
and we have:
[tex]F=qE[/tex] is the magnitude of the electric force. Since
[tex]E=4.30\cdot 10^4 V/m[/tex] is the magnitude of the electric field
[tex]q=32.0 nC = 32.0\cdot 10^{-9}C[/tex] is the charge
The electric force is
[tex]F=(32.0\cdot 10^{-9})(4.30\cdot 10^4)=1.38\cdot 10^{-3} N[/tex]
The displacement of the particle is
d = 0.660 m
Therefore, the work done is
[tex]W=Fd=(1.38\cdot 10^{-3})(0.660)=9.1\cdot 10^{-4} J[/tex]
C)
In this case, the angle between the direction of the field (upward) and the displacement (45.0° downward from the horizontal) is
[tex]\theta=90^{\circ}+45^{\circ}=135^{\circ}[/tex]
Moreover, we have:
[tex]F=1.38\cdot 10^{-3} N[/tex] (electric force calculated in part b)
While the displacement of the charge is
d = 2.50 m
Therefore, we can now calculate the work done by the electric force:
[tex]W=Fdcos \theta = (1.38\cdot 10^{-3})(2.50)(cos 135.0^{\circ})=-2.4\cdot 10^{-3} J[/tex]
And the work is negative because the electric force is opposite direction to the displacement of the charge.
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