If an object is thrown up at an initial velocity of 9.8 m/s , how long will it take to fall back to the ground?

t = 2 s

Explanation:

As we know that when object comes back to its initial position then the displacement of the object will be zero

so here we can say by kinematics equation

here we know that

now from above equation we know

so from above equation we have

t = 2 s

tube or goog with be a great resource to with that question

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 ! : )