Question

Compare the KE of an 80 kg person walking at 4 m/s with that of the same person moving at 6 m/s.

Answer 1

The correct answer is:
KE at 4 m/s less than KE at 6 m/s

In fact, the formula for the kinetic energy is:
$K= \frac{1}{2} mv^2$
where m is the mass of the person and v his speed.

When the person is moving at 4 m/s, his kinetic energy is:
$K= \frac{1}{2} (80 kg)(4 m/s)^2=640 J$
instead, when he's moving at 6 m/s, his kinetic energy is:
$K= \frac{1}{2}(80 kg)(6 m/s)^2=1440 J$

So, the kinetic energy at 4 m/s is less than the kinetic energy at 6 m/s.