A particle is moving in simple harmonic motion. At what displacement from equilibrium is its potential energy equal to its kinetic energy?
Correct: A
Potential energy U = (1/2)kx², and total energy E = (1/2)kA². Kinetic energy K = E - U = (1/2)kA² - (1/2)kx². Setting U = K gives (1/2)kx² = (1/2)kA² - (1/2)kx², so x² = A²/2, and x = A/√2.