The 500 kg car travelling at 25 m s-1 collides head-on with another of mass 800 kg travelling at 18 m s-1 in the opposite direction and they move together after impact. What is the magnitude of their velocity just after impact and in what direction do they move off?

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.

there are no contact forces mentioned on the list of choices that you've provided.