A spring hanging vertically is stretched by 0.14 Meters when a mass of 77.4 kg is hung from it. The mass is then placed on a smooth horizontal surface and pulled using the same spring. If the spring is now stretched by 0.02 Meters, what is the acceleration of the mass (in M/s2). I used the formula F=ma and got 9.81. I got it wrong. What am suppose to do with the spring length change?