$A$ stone dropped from a certain height takes $4$ seconds to reach the ground. The height is: (in $, m$)

$A$ boy is whirling a stone tied with a string in a horizontal circular path. If the string breaks,the stone

State the source of centripetal force that our earth requires to revolve around the sun. List the factors on which this force depends.

$(i)$ Why is Newton's law of gravitation called the universal law?
$(ii)$ What is the significance of this law in nature?

Newton's law of gravitation is called a universal law. Why?

Find the weight of an object at a height $6400 \, km$ above the earth's surface. The weight of the object at the surface of the earth is $20 \, N$ and the radius of the earth is $6400 \, km$. (in $, N$)