Two balls, $A$ and $B$ are thrown simultaneously, $A$ vertically upward with a speed of $20 \mathrm{~m} / \mathrm{s}$ from the ground and $B$ vertically downward from a height of 40 m with the same speed and along the same line of motion. At what points do the two balls collide by taking acceleration due to gravity as $9.8 \mathrm{~m} / \mathrm{s}^2$ ?

• A

  The balls will collide after 3 s at a height of 30.2 m from the ground
• B

  The balls will collide after 2 s at a height of 20.1 m from the ground.
• Correct answer
  C

  The balls will collide after 1 s at a height of 15.1 m from the ground
• D

  The balls will collide after 5 s at a height of 20 m from the ground

Hence, the correct answer is option: 'C'.