1. The problem statement, all variables and given/known data Ball 1 is dropped from rest at a height of 10m above the ground. at the same time, ball 2 is thrown straight upward from ground level with an initial speed of 10m/s. 2. Relevant equations find the relative velocity of the balls when they pass each other at t=1 second? equation given, relative velocity ==> v12= lv2-v1l vf=vi+at 3. The attempt at a solution since ball1 is falling, in respect to earth, the acceleration is possitive thus, v1f=v1i+at equals, vf= 0+9.8m/s^2 *1s vf= 9.8 m/s for ball 2 the ball is thrown upwards, thus being in a negative acceleration in respect to earth thus, v2F=v2i+a*t V2f= 10m/s+ (-9.8m/s^2)(1s) v2f= 0.2 now, lV2-V1l = 9.6m/s now, the correct answer is 10m/s and i wonder how come and why?? could it be that in respect to each other, their acceleration is negative? thus, resulting in v1=-9.8 v2=0.2 lv2-v1l = l0.2+9.8l = 10m/s?