Question

A 4kg mass moves with a velocity of 5m/s compute its kinetic energy

Answer 1

The kinetic energy of a moving object is given by
$K= \frac{1}{2} mv^2$
where
m is the mass of the object
v is its velocity

The object in our problem has a mass of m=4 kg and a velocity of v=5 m/s, so its kinetic energy is
$K= \frac{1}{2}mv^2 = \frac{1}{2}(4 kg)(5 m/s)^2=50 J$