Help with two quick electric potential and voltage problesm

In summary, to move a -6.0 µC charge from ground to a point with a potential of +7.00 V, 0.000042 J of work is needed. When starting from rest 74.5 cm away from a fixed point charge with Q = -0.150 µC, an electron will be moving at a speed of 2.30311e7 m/s when it reaches a very far distance. The correct formula for (2) is W = K*(qQ/r), where q is the charge of the electron and Q is the fixed charge. No minus sign is needed in (2) since directions are not involved.
  • #1
jhcollaz
3
0

Homework Statement



1) How much work is needed (done by the field) to move a -6.0 µC charge from ground to a point whose potential is +7.00 V higher?

2)An electron starts from rest 74.5 cm from a fixed point charge with Q = -0.150 µC. How fast will the electron be moving when it is very far away?

It says my answer is not right. I only have two attempts at these problems so I am not sure what to do. Do i include the sign of the charge?

Homework Equations



For (1)

w=q*v

For (2)

W = (1/2)*m*V^2 -(1/2)*m*V^2
W = K*(qQ/r)

The Attempt at a Solution



(1)
w=q*v
=(6*10^-6) * 7
= 0.000042 J

(2)
W = K*(qQ/r)
=(9*10^9)* ( ((1.6*10^19)*(0.125*10^-6)) / 0.745 )
W = 2.41611*10^-16

W = (1/2)*m*V^2 -(1/2)*m*V^2
2.41611*10^-16 = (1/2)*(9.11*10^-6)*V^2 -0
v = 2.30311e7
 
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  • #2
I would include a minus sign on (1) because work is done by the potential as it attracts the negative charge to the positive plate.
In (2), you wrote .125 for the charge when it says .15 in the question, and it has thrown off your answer. No minus in (2) since directions are not involved.
 

1) What is electric potential?

Electric potential is a measure of the amount of electric potential energy per unit charge at a given point in an electric field.

2) How is electric potential different from voltage?

Electric potential is a scalar quantity, while voltage is a measure of the difference in electric potential between two points. In other words, voltage is the potential difference between two points, while electric potential is the potential energy per unit charge at a single point.

3) How do you calculate electric potential?

Electric potential can be calculated by dividing the electric potential energy by the charge at a given point in an electric field. The equation is V = U/q, where V is electric potential, U is electric potential energy, and q is charge.

4) What is the unit of electric potential and voltage?

The unit of electric potential and voltage is the volt (V). It is equivalent to joules per coulomb (J/C).

5) How is electric potential related to electric field?

Electric potential is directly proportional to electric field. In other words, the direction of the electric field is the direction in which electric potential decreases. This means that electric charges will tend to move from areas of higher electric potential to areas of lower electric potential.

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