You wish to push a cart across a frictionless surface, so you
apply a 20.0 N force for a period of 3.0 seconds. As a result,
the cart goes from rest to a velocity of 2.3 m/s.
What is the mass of the cart?

it doesn't. it was imagined up in the middle ages.

d) physical means can be used to separate the components of air.

that tool is called an altimeter which measures your altitude which can be used to tell which atmosphere you are currently in, including the stratosphere.

hope this ! : )

i don't understand. explain it clearly