If the diameter of the earth becomes two times its present value and its mass remains unchanged,then how would the weight of an object on the surface of the earth be affected?

$A$ stone is dropped from the top of a tower. Its speed after it has fallen $20 \, m$ is (Take $g = 10 \, m s^{-2}$): (in $, m s^{-1}$)

The weight of any person on the moon is about $1/6$ times that on the earth. He can lift a mass of $15\, kg$ on the earth. What will be the maximum mass,which can be lifted by the same force applied by the person on the moon (in $, kg$)?

Earth is continuously pulling the moon towards its centre,still it does not fall to the earth,why?

Two objects of masses $m_1$ and $m_2$ having the same size are dropped simultaneously from heights $h_1$ and $h_2$ respectively. Find out the ratio of time they would take in reaching the ground. Will this ratio remain the same if $(i)$ one of the objects is hollow and the other one is solid and $(ii)$ both of them are hollow,size remaining the same in each case. Give reason.

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