1. The problem statement, all variables and given/known data Projectile motion questions, Kinematics questions: my physics teacher defined acceleration due to gravity as -9.81 m/s2. Specifically in questions regarding: dropping an object, throwing an object downwards, obliquely launching an object. Today we are studying a box on an inclined plane question, and for some reason Fg = mg and the gravitational (9.81) was NOT negative. Can someone please explain: Let me give you my attempt at the question 3. The attempt at a solution a box is on the top of a ramp with an inclination of 35˙. It is released from rest and it begins to accelerate down the ramp. The mass of the box is 1.5kg and the force of friction between the box and the ramp is 2.6N. What is the acceleration of the train down the ramp? Step 1: Find the force of gravity on the train (Fg on the diagram) Fg=mg =(1.5kg)(9.81) =14.7N IF I MADE THIS: Fg=mg =(1.5kg)(-9.81) =-14.7N Step 2: Find the Fgx Fgx= Fgsin =(14.7N)(sin35o) = 8.43N THEN THIS WOULD BE: Fgx= Fgsin =(-14.7N)(sin35o) = -8.43N Step 3: Calculate the force of train. Fnet = Fgx – Ffriction Fnet = 8.43N - 2.6N Fnet= 5.83N THEN THIS WOULD BE Fnet = -8.43N - 2.6N Fnet= -11.03N Step 4: Find the acceleration Fnet=ma 5.83N=(1.5kg)(a) 3.89m/s2=a THEN THIS WOULD BE -11.03N = (1.5kg)(a) a=-7.35 m/s2 WHICH IS WRONG! Please help.