**Q1: **

The graph shows the kinetic energy,
,
against the speed, ,
of two objects, and .
The relativistic kinetic energy of object
is shown by the red line,
whereas the classical kinetic energy of object
is shown by the blue line. Object
has a rest mass
and object has a rest mass
.
The speed of light, , is defined to be 1.

Which object has a greater rest mass?

At a speed of ,
the classical kinetic energy of object
has the same value as the relativistic kinetic energy of
object . The formula
can be used to work out the rest mass of object
from the rest mass of object , where
. If
kg,
what is the rest mass of object ?