Question
An electron and a proton are detected in a cosmic ray experiment, the first with kinetic
energy 10 keV, and the second with 100 keV. Which is faster, the electron or the
proton ? Obtain the ratio of their speeds. (electron mass = 9.11×10-31 kg, proton mass
= 1.67×10–27 kg, 1 eV = 1.60 ×10–19 J).
Solution
Given that,
Kinetic energy, 
K.E of proton, 
K.E is given by,
∴ ratio of their speed is given by,
= 13.54
Thus electron is faster than proton by a magnitude of 13.54.
