Prove that conservation of four-momentum forbids a reaction in which an electron and positron annihilate and produce a single photon (y-ray). prove that the production of two photons is not forbidden.

Automobile fuel efficiency is often measured in miles that the car can be driven per gallon of fuel (mpg). heavier cars tend to have lower fuel efficiencies (lower mpg ratings). which variable (weight or fuel efficiency) is most naturally considered the explanatory (predictor) variable in this context?

Alarge box of mass m is pulled across a horizontal frictionless surface by a horizontal rope with tension t. a small box of mass m sits on top of the large box. the coefficients of static and

To a of 4 x hz is 1. 0. mm nm nm