The weight of an object:

$A$ stone is released from the top of a tower of height $19.6 \, m$. Calculate its velocity just before touching the ground.

Give reason:
$(a)$ Value of '$g$' is not constant on Earth.
$(b)$ Objects with different masses take the same time to fall from a fixed height.
$(c)$ '$G$' is known as the universal gravitational constant.

Give an example of the motion of an object under the influence of gravitational force on Earth.

$(i)$ Seema buys a few grains of gold at the poles as per the instructions of one of her friends. She hands over the same when she meets her at the equator. Will the friend agree with the weight of gold bought? If not,why?
$(ii)$ If the moon attracts the earth,why does the earth not move towards the moon?

The mass of the planet Jupiter is $1.9 \times 10^{27} \, kg$ and that of the Sun is $1.99 \times 10^{30} \, kg$. The mean distance of the Sun from Jupiter is $7.8 \times 10^{11} \, m$. Calculate the gravitational force which the Sun exerts on Jupiter.