28 1 Introduction to Modern Physics
5. After dividing (1.43) by (2mv) we obtain the following expression
รูป. (1.44)
The expression for the kinetic energy EK in (1.40) using (1.44) can be written as follows:
รูป , (1.45)
xi mo
since dx/dt is the particle velocity υ by definition and the masses m and mo correspond to particle positions xi and xf, respectively.
1.20.4 Total Relativistic E as a Function of Momentum p
The expression for the total relativistic energy E as a function of the relativistic momentum p is as follows:
รูป . (1.46)
Equation (1.46) is obtained from Einstein’s expression for the relativistic mass given in (1.31) as follows:
1. Square the relationship for the relativistic mass m of (1.31), multiply the result by c4 and rearrange the terms to obtain
m2c4 − m2c2υ2 = m2oc4 .
2. Equation (1.47) can be written as
(1.47)
รูป(1.48)
or
, (1.49)
using the common relativistic relationships for the total energy E, rest energy Eo and momentum p, i.e., E = mc2, Eo = moc2, and p = mυ.
The following two relationships are also often used in relativistic mechanics: