elastic collision in one dimension 1. The problem statement, all variables and given/known data Block 1 of mass m1 slides along an x axis on a frictionless floor with a speed of 2.40 m/s. Then it undergoes a one-dimensional elastic collision with stationary block 2 of mass m2 = 2.00m1. Next, block 2 undergoes a one-dimensional elastic collision with stationary block 3 of mass m3 = 2.00m2. what is the speed of block 3? the answer is 1.78. i just can't figure it out. more questions that relate to problem...are the speed, kinetic energy, and the momentum of block 3 greater than or less than, or th same as the initial values for block one? the answers are less, less, greater... but i don't need help with them because i haven't attempted them yet. 2. Relevant equations v1f = m1 - m2 / m1 + m2 * v1i v2f = 2m1 / m1 + m2 *v1i 3. The attempt at a solution v1f = v2i = m1 - m2 / m1 + m2 * v1i = m - 2m/ m + 2m *4 = -m/3m * 4 = -4/3 v2f = v3i = 2m1 / m1 + m2 * v1i = 2m / m +2m *4 =2/3 *4 =8/3 v3f = m2 - m3 / m2 + m3 * v2i = 2 - 4 / 2 + 4 * (-4/3) = -2/6 (-4/3) =-8/18 clearly this is wrong. i really did try a lot of different things. what am i doing wrong? when i multiply (4/3) by (8/3) and divide by 2, i get the right answer! but that's just luck.