1. The problem statement, all variables and given/known data a 8kg ball is hanging from a 1.35m string. A 2 kg ball moving horizontally at 5m/s hits the hanging 8kg ball in an elastic collision. What is the tension in the string just after the collision? 2. Relevant equations 3. The attempt at a solution Initially there is only a gravitational force of 8*9.8 = 78.4 N. Using conservation of momentum, we can find that the ball has a velocity of 1.25 m/s just after the collision. so the centripetal acceleration is v^2/r = 1.1574 m/s^2. That centripetal acceleration is due to a centripetal force point in the opposite direction as the gravitation force so F_g - M*a_c = answer 78.4 - (8)*(1.1574) =69.14 Newtons The back of the book says the answer is 102 Newtons. I feel like I worked this out right as far as my understanding of physics goes, but then I think about it and I feel like the tension should increase. Even if I add the centripetal force to the gravitational force I come up short of 102 N. Help?