A body weighs $72\; N$ on the surface of the earth. What is the gravitational force on it, at a height equal to half the radius of the earth ?

If the value of g at the surface of the earth is $9.8$ $m/{\sec ^2}$, then the value of g at a place $480\, km$ above the surface of the earth will be .......... $m/{\sec ^2}$. (Radius of the earth is $6400\, km$)   

Which of the following statements is true

A projectile is fired from the surface of the earth with a velocity of $5\, ms^{-1}$ and angle $\theta$ with the horizontal. Another projectile fired from another planet with a velocity of $3\, ms^{-1}$ at the same angle follows a trajectory which is identical with the trajectory of the projectile fired from the earth. The value of the acceleration due to gravity on the planet is (in $ms^{-2}$) is (given $g = 9.8\, m/s^2$)

The ratio of the radius of the earth to that of the moon is $10$. The ratio of acceleration due to gravity on the earth and on the moon is $6$. The ratio of the escape velocity from the earth's surface to that from the moon is