Question

At what speed will the mass of a body be 1.25 times its rest mass?
(A) 0.1c
(B) 0.3c
(C) 0.40
(D) 0.6c​

Answer 1

Answer:

the answer is 0.40 which is cm i think answer is c

Answer 2

Answer:

The speed of a body is 0.6c

Explanation:

Given, the mass of a body be 1.25 times its rest mass i.e.,$m= 1.25 m_{0}$

The mass of a moving electron is

$m=\frac{m_{0}}{\sqrt{1-\frac{v^{2} }{c^{2} } } }$

where v is velocity, c is the velocity of light through vacuum, and $m_{0}$ is the rest mass

If $m=1.25m_{0}$, then the

$1.25m_{0}=\frac{m_{0}}{\sqrt{1-\frac{v^{2} }{c^{2} } } }$

$\implies 1.25=\frac{1}{\sqrt{1-\frac{v^{2} }{c^{2} } } }$

$\implies {1-\frac{v^{2} }{c^{2} } } =\frac{1}{1.56}$

$\implies \frac{v^{2} }{c^{2} } } =0.36$

$\implies v =0.6c$

Therefore, the speed of a body is 0.6c

Hence, the correct answer is option (D).