Question Detail
Question
An electron starts from rest and falls through a potential rise of 80 V. As calculated in Solved Problem 25.4, what is its final speed?
Correct Answer
Option B is the correct answer.
Detailed Explanation
From Solved Problem 25.4: The change in PEE = Vq = (80 V)(-1.6 × 10⁻¹⁹ C) = -1.28 × 10⁻¹⁷ J. This lost PEE appears as KE, so ½mv² = 1.28 × 10⁻¹⁷ J. Using m = 9.1 × 10⁻³¹ kg, v = √[(2 × 1.28 × 10⁻¹⁷ J) / (9.1 × 10⁻³¹ kg)] = 5.3 × 10⁶ m/s.
Hint
Relate the change in potential energy to the kinetic energy gained. Recall the charge and mass of an electron.