If gravity is the only force present, what is the total mechanical energy of a
rock falling off a cliff at a time when its potential energy is 500 J and its
kinetic energy is 600 J?
A. 500 J
B. 100 J
C. 600 J
D. 1,100 J

(D) is correct option.

Explanation:

At a particular time, the potential energy of a rock is 500 J and its kinetic energy is 600 J.

It is required to find the mechanical energy of the rock. Mechanical or total energy is the sum of kinetic and potential energy. So,

TE = K+ P

TE = 500 J + 600 J

TE = 1100 J

So, the total mechanical energy of a  rock is 1100 J. Hence, the correct option is (D).

this is poiselle's equation from fluid mechanic in physics. mech eng