Question

Suppose an object that is initially not moving is dropped to fall freely downward. What can we say about its energy?  

		a) The kinetic energy increases.
		b) The potential energy decreases (becomes more negative if initially zero).
		c) The total energy increases.

Answer 1

Solution:

Let us go to the basics first.

Case: An object (that is initially not moving) is dropped to fall freely downward.

As object was initailly not moving, so its Kinetic energy, KE was zero.

As object starts to fall freely downward, so it attains a velocity due to downward gravitational force, which increases its kinetic energy now.

Also, from Conservation of energy:
Total energy = KE + PE = constant

=> As kinetic energy is now increasing, so potential energy (PE) must decrease to meet law of conservation of energy validity.

Thus, a) The kinetic energy increases. ===> (TRUE)

b) The potential energy decreases (becomes more negative if initially zero). ===> (TRUE)

c) The total energy increases.===> (FALSE)

Thanks!!!