Question Detail
Question
An electron starts from rest and falls through a potential rise of 80 V. What is its final speed? (m_e = 9.1×10⁻³¹ kg, e = 1.6×10⁻¹⁹ C)
Correct Answer
Option A is the correct answer.
Detailed Explanation
Kinetic energy gained = qV = (1.6×10⁻¹⁹ C)(80 V) = 1.28×10⁻¹⁷ J. Then ½ mv² = KE → v = √(2KE/m) = √(2.56×10⁻¹⁷ / 9.1×10⁻³¹) ≈ 5.3×10⁶ m/s.
Hint
½ mv² = qV.