アメリカ在住で、娘の物理のテスト勉強を手伝っています。 Bが正解なのですが、なぜだかわかりません。解説お願いいたします。 Cosmic rays bombard Earth’s upper atmosphere, creating subatomic particles called muons, which then stream toward the surface of Earth at nearly the speed of light. The muon is not a nucleon. It is an unstable fundamental particle with most properties the same as those of an electron but with a larger mass. In a frame of reference at rest with respect to the muon, the muon decays with a half-life of approximately . In the most common form of muon decay, the total mass of the measured products is found to be much less than the mass of the muon. Which of the following best explains the measured discrepancy in mass? A) The energy equivalent of the lost mass is transferred to the products, so they have a greater total potential energy than the muon had. B) The energy equivalent of the lost mass is transferred to the products, so they have a greater total kinetic energy than the muon had. C) Relativistic effects cause the total muon energy to be measured as larger and the total product energy to be measured as smaller than the same measurements in the reference frame of the particles. D) Relativistic effects cause the muon mass to be measured as larger and the product masses to be measured as smaller than the same measurements in the reference frame of the particles. Answer B Correct. When the muon decays, some mass is converted to energy. This energy becomes kinetic energy of the products. Answer C Incorrect. Relativistic effects may cause observers in different reference frames to measure different energies. However, conservation of energy applies in every reference frame. Measurements will not show that energy is conserved in one frame but not another.
物理学
