Anotebook sitting on a desk has 19 j of potential energy. what is the total mechanical energy of the notebook?

The total mechanical energy of the notebook is 19J.

Mechanical energy is the sum of potential energy and kinetic energy.  It has no kinetic energy, because it's not moving.  So its potential energy is all the  mechanical energy it has.

answer: the exterior temperature of commercial jet planes as they leave the stratosphere and return to the ground increases steadily.

explanation:

the lower most layer of atmosphere is troposphere which extends from 0 to 12 km above the surface of the earth. the temperature initially decreases as distance is increased from the earth's surface. commercial jets fly in lower part of the stratosphere. the stratosphere extends upto 50 km. the temperature in stratosphere starts rising again due to presence of ozone which traps the uv rays.

thus, when the planes leave the stratosphere and return to the ground, the exterior temperature increases steadily.

i think they are all correct

explanation:

they seem good