How can one solve numericals about gravity?

There are a number of questions that may involve gravity. The questions could relate to the motion of an object dropped from some height or thrown with some initial velocity. Questions involving gravity may also relate to the weight of a substance. 

To solve such numerical problems, one can use the equations of motion:

v = u + at

s = ut + 1/2 at^2

v^2 = u^2 + 2as

where u and v are the initial and final velocities respectively, a is the acceleration, s is the distance traveled and t is the time taken.

Note that in questions involving gravity, the acceleration of the object (unless otherwise stated) is equal to the acceleration due to gravity. It is denoted as g and has a value of 9.8 m/s^2. 

It is important to use the right sign with g. For an object moving upwards from Earth's surface, the gravity will oppose the motion and acceleration will be equal to -g. For an object moving towards the surface of Earth, a = g.

Also, note that an object thrown upwards comes to a full stop and then starts its descent.

And finally, the weight of an object is given by Newton's second law as:

weight = mass x g.

Hope this helps.