Confusing question...?

Question

A particle with rest mass m moves with speed 0.6c. Its kinetic energy is:

a) 0.18mc^2
b) 0.22mc^2
c) 0.25mc^2
d) mc^2
e) 1.25mc^2

Answer 1

In relativistic situations, the total energy is:

E = mc^2/sqrt(1 - (v/c)^2)
= mc^2/(sqrt(1-0.36) = mc^2/sqrt(0.64) = mc^2/(0.8)
= 1.25 mc^2

Since the rest-energy is mc^2, the kinetic energy is

KE = E - mc^2 = 0.25 mc^2
Answer c).

Answer 2

The answer is (a)... I think...
Ke=0.5 mV^2
Ke= 0.5 m (.6c)^2= .18mc^2