Question

1. the starting line of a cross country foot race is at the bottom of a hill. which form(s) of mechanical energy of the runners will change when the starting gun is fired?

a. kinetic energy only
b. potential energy only
c. both kinetic and potential energy
d. neither kinetic nor potential energy

Explanation:

Mechanical energy has two main forms: kinetic energy (energy of motion, $KE = \frac{1}{2}mv^2$) and potential energy (e.g., gravitational potential energy, $PE = mgh$). Initially, at the starting line (bottom of the hill), runners are at rest, so $KE = 0$, and $PE$ depends on their height (constant at the bottom). When the gun fires, runners start moving (velocity $v$ increases), so $KE$ increases. As they run up the hill, their height $h$ changes, so $PE$ (gravitational) also changes. Thus, both kinetic and potential energy change.

Answer:

c. Both kinetic and potential energy