複選題21. Two balls of masses my = 1 kg and mo = 100 kg, with initial speed 1 m/s and 10 m/s, respectively, collide inelastically in space. They stick together after the collision. Which of the following is true in the Center of Mass Frame? (A) The total momentum does not change； (B) The total kinetic energy does not change； (C)The magnitude of velocity change of me is less than that of mi； (D) The magnitude of momentum change of me is less than that of my； (E) The magnitude of kinetic energy change of me is less than that of my.

複選題22. Consider a damped harmonic oscillator, which of the following is true?(A) If it is underdamped, the resonant frequency increases with larger damping； (B) If it is underdamped, the amplitude decays faster with larger damping； (C)If it is underdamped, and is driven by an external sinusoidal force, the amplitude of the oscillation is maximum if the frequency of the force is the same as the resonance frequency； (D) In order to damp the kinetic energy and the elastic energy as fast as possible, one should design the oscillator to be at critical damping condition； (E) If it is overdamped, the system does not oscillate and returns to the equilibrium position slowly.

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