Kinetic Energy: Particle Motion, Reference Frames, and Systems

All flashcards

What is classical kinetic energy?

For a particle of mass $m$ and speed $v$, kinetic energy is $K = \frac{1}{2}mv^2$.

How is the kinetic energy of a particle system calculated?

Add the kinetic energies of its particles: $K_{\text{system}} = \sum_i \frac{1}{2}m_i v_i^2$.

How can kinetic energy be calculated from momentum?

For a particle of momentum $p$ and mass $m$, $K = \frac{p^2}{2m}$.

Why does kinetic energy depend on the reference frame?

The measured speed can differ between frames, and kinetic energy depends on the square of that speed.

What is internal kinetic energy?

Kinetic energy described relative to a frame attached to or moving with a system.

Quiz questions

1. What is the classical kinetic energy of a particle with mass $m$ and speed $v$?Answer: $K = \frac{1}{2}mv^2$
2. Which expression gives a particle's kinetic energy from its momentum $p$ and mass $m$?Answer: $K = \frac{p^2}{2m}$
3. A 2-kg object moves at 3 m/s. What is its kinetic energy?Answer: 9 J
4. At what speeds is the classical kinetic-energy formula applicable?Answer: At speeds much less than the speed of light.
5. How is the total kinetic energy of a system of particles determined?Answer: By summing the kinetic energy of each particle.