Two balls, A and B, are thrown simul¬taneously, A vertically upward with a speed of 20 m/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 m/s*?

To find the collision point, we analyze the relative motion of the two balls. Ball A is thrown upward with initial velocity u_A = 20 m/s, and Ball B is thrown downward with u_B = -20 m/s from a height of 40 m. The relative velocity between them is the sum of their speeds, v_rel = 20 + 20 = 40 m/s, because they move toward each other and the acceleration due to gravity (g = 9.8 m/s") cancels out in relative terms. The time to collide is t = distance / v_rel = 40 / 40 = 1 second. To find the height from the ground, we use the equation of motion for Ball A: h = ut - (1/2)gt". Substituting the values, h = (20!! 1) - (0.5!! 9.8!! 1") = 20 - 4.9 = 15.1 m. Thus, the balls collide after 1 second at a height of 15.1 m from the ground.