More Conservation of Energy Problems Video Lessons

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# Problem: What potential difference is needed to stop an electron that has an initial velocity V = 6.0 × 105 m/s?

###### FREE Expert Solution

Law of conservation of energy:

$\overline{){{\mathbf{K}}}_{{\mathbf{i}}}{\mathbf{+}}{{\mathbf{U}}}_{{\mathbf{i}}}{\mathbf{+}}{{\mathbf{W}}}_{{\mathbf{nc}}}{\mathbf{=}}{{\mathbf{K}}}_{{\mathbf{f}}}{\mathbf{+}}{{\mathbf{U}}}_{{\mathbf{f}}}}$, where Wnc is the work done by non-conservative forces such as friction.

In this case, we do not have Wnc since there are no non-conservative forces.

Wnc = 0

Since the electron is in motion, the initial potential energy is zero.

Ui = 0

Also, Kf = 0 since the electron is coming to rest.

Kinetic energy is expressed as:

$\overline{){\mathbf{K}}{\mathbf{=}}\frac{\mathbf{1}}{\mathbf{2}}{{\mathbf{mv}}}^{{\mathbf{2}}}}$

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###### Problem Details

What potential difference is needed to stop an electron that has an initial velocity V = 6.0 × 105 m/s?