Question

plz explain this para

Answer 1

this para wants to explain the fact that as you or any object approach the speed of light, the Newtonian mechanics begin to fail.
so you can not simply use Newton's laws equations for for objects traveling with speeds comparable to the speed of light.
This is a consequence of Einstein relativity that, as object approach speed of light, mass increases as compared to its rest mass.
given by equation,
$\\ m = \frac{m_{o}}{ \sqrt{1 - \frac{ {v}^{2} }{ {c}^{2} } } }$
m is mass of object when it's moving, m° is rest mass, v is speed of object
caution: motion is relative, so what seems to be at rest from one observer, can in uniform or accelerated motion for other observers.

Thanks for asking this question.