Answer is simple. I have assumed that you lifted both the balls and they were released after a time interval. The first ball strikes causing the last ball to rise , then the second one strikes casusing the second - last to rise up. Note that this will only happen if the second ball hits the first one just just & just after it collides with the first. At one point , the velocity of the first ball during collision is zero. Thus it is like lifting one ball and striking. Use collisions equations and brood at the magnitude of the force "travelled" to the last ball during the course of all the collisions. Please note that the balls have to fight gravity to rise up , so the oribablity of two shots in one hit is not so possible (Especially if the BALL IS RELEASED AND NOT THROWN WITH A INITIAL VELOCLTY).
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