A ball is dropped from top of a tower of 100 m height. Simultaneously another ball was thrown upward from bottom of the tower with a speed of 50 ~m / s . They will cross each other after (g=10 ~m / s ^2 )

Step-by-step solution

Let the two balls cross each other after time t . Height covered by first ball h₁= 1 2 g t^2 Height covered by second ball h₂=u t- 1 2 g t^2 but h₁+h₂=100 aligned 1 2 g t^2+u t- 1 2 g t^2 & =100 u t & =100 50 t & =100 t=2 ~s aligned