1. A student who's standing still on level ground weights 570 N and is wearing a backpack that is 81 N. a) What's the magnitude of net force on the student? b) What's the magnitude of the contact force on the student by the backpack? c) What's the magnitude of the contact foce on the student by the ground? 3. I understand both parts A (net foce = zero because there is no acceleration) and C (contact forceon the student by the ground = 651 N) in the equation, I'm just having a difficult time understand part b) with the horizontal forces. My thoughts lead me to think that the contract force on the student by the backpack would have been 570 N - 81 N = 489 but apparently that's wrong. can anyone help and explain? Thank you!!