At one point in space, the electric potential energy of a 15 nc charge is 42 μj . part a) what is the electric potential at this point?
express your answer to two significant figures and include the appropriate units.
part b) if a 20 nc charge were placed at this point, what would its electric potential energy be?
express your answer to two significant figures and include the appropriate units.

Part A:

Part B:

Explanation:

Part A:

The potential energy at a point due to a charge is defined as

.

where,

V = electric potential at that point.

Therefore,

Part B:

Now, if the charge at that point is replaced with , then the electric potential energy at that point is given by

see the picture for the vector

the magnitude of the vector by pythagorean theorem

r = √( (-10)^2 + (3)^2 ) = √109

magnitude = √109 units

the direction angle between vector and x-axis is

tan^(-1)(3/10) = 16.699

so the direction is approximately 16.7 degrees north of west