**Answer: **When a ball is thrown upwards, its velocity is decreased due to the gravitation of the earth, reaching zero after reaching a certain height. From there, the ball then starts to fall. Maximum height of the ball is dependent upon its initial velocity.

According to Newton’s third equation of motion,

v^{2} = u^{2}+2as, with v = the final velocity of the ball = 0 and a = – g

Therefore, 0 = u^{2} + 2 (-g) s and maximum height of the ball = s = -(u^{2}/ 2g)

Hence, when the initial velocity u is higher, the larger is the height reached by the ball.

For this reason the higher the initial velocity, the ball will oppose the gravity of the earth more and larger will be the height to which it can reach. The value of g keeps decreasing as we go higher above the surface of the earth. Thus, the force pulling the ball downward decreases as the ball goes up. Keep increasing the initial velocity of the ball, till it reaches larger and larger heights.

Above a particular value of initial velocity of the ball, the ball is able to overcome the downward pull of the earth and escape the earth forever without falling back to the earth. This velocity is called escape velocity. We can determine its value by using the law of conservation of energy.