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:
[tex]K= \frac{1}{2} mv^2[/tex]
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:
[tex]K= \frac{1}{2} (80 kg)(4 m/s)^2=640 J[/tex]
instead, when he's moving at 6 m/s, his kinetic energy is:
[tex]K= \frac{1}{2}(80 kg)(6 m/s)^2=1440 J [/tex]
So, the kinetic energy at 4 m/s is less than the kinetic energy at 6 m/s.
