A force F pushes on three boxes that slide without friction on a horizontal surface, as indicated in the Figure . Box 1 has a mass of 1 kg, box 2 has a mass of 2 kg, and box 3 has a mass of 3 kg. The boxes are in contact, and slide as a group with an acceleration a. Is the magnitude of the force of contact between boxes 1 and 2 greater than, less than, or equal to the magnitude of the force of contact between boxes 2 and 3? Explain 3 2 a 3 kg F 2 kg 1 kg