You are pulling your little sister on her sled acroos an icy(frictionless) surface. When you exert a constant horizontal force of 110 N, the sled has an acceleration of 2.5 m/s^2. If the sled has a mass of 7 kg, what is the mass of your little sister? Heres how I attempted it: F=110N A=2.5 m/s^2 M1= 7kg M2= ? F=(M1+M2) A M2= 41.2 kg The answer is 37 kg, but I can't figure out how to arrive at this mass. Can anyone help me?