Calculating change in energy of a particle

[x86]

Homework Statement

An electron moves from an initial location between parallel plates where the electric potential is Vi = 30 V and Vf = 150 V

a) Determine the change in the electrons potential energy

2. Equations
J/C = V = N/C * m

The Attempt at a Solution

a) The electron is naturally moving to a location of higher energy, therefore its potential energy decreases as its kinetic energy increases.

Potential energy change = Ep2 - Ep1 = Vfq - Viq = q(Vf-Vi) = q(120 V) = -1.92 * 10^-17 J.

The sign makes sense to me, since the electron has more potential energy at Vi than Vf.

However, the book says the answer is +1.92*10^-17 J. Can someone help me out with why I am is wrong? Thanks

 

[Fightfish]

Well your book looks like its wrong. Your qualitative reasoning seems correct to me.

 

[rude man]

Are you sure they didn't ask for the change in kinetic energy? Because otherwise I have to agree with your answer as being negative.

 

[x86]

Yes I'm sure they asked for potential energy. I guess the book is wrong. Thanks for confirming this.

 

[Nickie]

Your solution is correct, the book may have made a mistake. The change in potential energy should indeed be negative, as the electron is moving from a location of higher potential to a location of lower potential. This means that the electron is losing potential energy and gaining kinetic energy. The sign of the change in potential energy is important as it indicates the direction of energy flow. In this case, the negative sign indicates that energy is leaving the system. Therefore, your solution is correct and the book's answer is likely a mistake.