1. The problem statement, all variables and given/known data The system shown is released from rest and moves 50 cm in 1.0 s. What is the value of M? All surfaces are frictionless. X = 0.5 m t = 1sec m1 = 3kg m2 = M However, my question is about the acceleration. I'm just curious why I cannot use vf = v0 + at equation instead of x = x0 + v0t + 0.5at^2 2. Relevant equations x = x0 + v0t + 0.5at^2 vf = v0 + at 3. The attempt at a solution X = X0 + V0t + 0.5at^2 0.5m = 0 + 0 + 0.5a(1)^2 a=1m/s^2 M*g = (3kg + M)a M(g-a) = 3a M = 3a/(g-a) = 0.34kg So I got M = 0.34kg. I know this is the answer but now my question is the acceleration. I know I got 1m/s^2 from X = X0 + V0t + 0.5at^2 equation, but why can I not use Vf = V0 + at equation? If I use Vf = V0 + at then I get a=0.5m/s^2 since vf = 0.5m/s and v0 = 0m/s and t=1. Why do they have different acceleration?