# Mass and Total Energy

2. A point source of neutrons, of strength S = 108 cm-2s-1, is located at point (x1, y1, z1) = (-10 cm, 20 cm, 0). Calculate the neutron flux and current (magnitude and direction) at the point (x, y, z) = (50 cm, 40 cm, 0). As in Problem 1, take D = 1 cm and L = 5 cm. Solution:

Note: In the problems below, take c = 3.0*108 m.s-1.

3. Neutrons have a rest mass of 1.6749*10-27 kg (equivalent to 939.6 MeV). (a) A neutron has a total energy 945 MeV, what are its relativistic mass in MeV, its speed in m/s, its kinetic energy, and its momentum in kg.m.s-1? (b) Repeat the exercise for neutrons of total energy 960 MeV, 980 MeV, 1000 MeV Display all results in a Table.

Solution:

Total Energy (MeV)| Relativistic Mass (MeV)| Speed (m/s)| Kinetic Energy (MeV)| Momentum (kg.m.s-1)| 945| 945| 3.203*107| 5.4| 5.395*10-20|

960| 960| 6.150*107| 20.4| 1.053*10-19|

980| 980| 8.525*107| 40.4| 1.489*10-19|

1000| 1000| 1.027*108| 60.4| 1.830*10-19|

4. [Lamarsh p. 46 Problem 18 + a new part] An electron starting from rest is accelerated through a potential difference of 8 million volts. (a) What is its final kinetic energy?

(b) What is its total energy?

(c) What is its final mass?

(d) What is its speed, in m/s and as a fraction of c?

Solution:

5. [Lamarsh p. 47 Problem 25] An electron moves with a kinetic energy equal to its res-mass energy....

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