Question

A rock is dropped from a third story window to the ground below. Assuming air resistance can be ignored, as it falls: a) only its kinetic energy is conserved.
b) only its momentum is conserved.
c) both its kinetic energy and its momentum are conserved.
d) only its mechanical energy is conserved.
e) both its mechanical energy and its momentum are conserved.

Answer 1

Answer:

Option d) only its mechanical energy is conserved

Explanation:

Since, mechanical energy of a system is the sum of its kinetic energy and potential energy.

Potential energy depends directly on height while kinetic energy depend on the speed of the body.

When the rock is dropped its potential energy decreases while its kinetic energy increases while the potential energy is maximum at the top and kinetic energy was zero.

Therefore, these two energies are inter convertible and when one increases the other decreases and vice-versa keeping the overall mechanical energy conserved.