An electron has a kinetic energy of 1.264 MeV. Using the kinetic energy formula EK = mc2 - mc02, where m is the mass of the electron and c is the speed of light, the speed of the electron can be calculated. The speed is found to be 0.957c, where c is the speed of light in a vacuum.

1. 1
An electron is moving
with a kinetic energy of
1.264 MeV.
What is its speed?

2. 2
Helping Tools
No.1

3. 3
No.2
Solution

4. 4
2
1.624 0.511
1.775 1775000
E K mc MeV MeV
MeV eV
= + = +
= =

5. 5
2
2 2
2 2
2 2
2 2
0.511
1.775
1 1
1.775 1 0.511 1 0.29
mc MeV
E MeV
u u
c c
u u
c c
=  =
− −
 − =  − =

6. 6
2 2 2 2 2
2 2
0.29 0.0841
(1 0.0841) 0.957
c u c c u c
c u c u
 − =  − =
 − =  =
The End