A stone ‘A’ is dropped from the top of a tower 20 m high simultaneously another stone ‘B’ is thrown up from the bottom of the tower so that it can reach just on the top of tower. What is the distance of the stones from the ground while they pass each other.


Correct option is

15 m


Let ‘t’ be the time when they pass one another

From (1) and (2) we get


Stone B can reach just on the top of tower.

We can calculate the velocity of stone B,




From eq (1) the required distance from the ground is


          = 15 m




A rider on an open platform, which is descending at constant speed of 3 ms-1, throws a ball. Relative to platform, ball’s initial velocity is horizontal at 12 m/s. The ground is 10 m below the location where the ball is thrown:

(i):-Where does the ball hit the ground?

(ii):-How long after the ball hits the ground does the platform reach ground level?

(iii):-With what velocity does the ball hit the ground?


A freely falling body, falling from a tower of height h covers a distanceh/2 in the last second of its motion. The height of the tower is (take g = 10 ms–2) nearly