1. The problem statement, all variables and given/known data A 5400 kg helicopter accelerates upward at 2.17 m/s2. The acceleration due to gravity is 9.8 m/s2. What life force is exerted by the air on the propellers? Answer in N. 2. Relevant equations Fnet=ma 3. The attempt at a solution I am making the acceleration positive (2.17m/s2) and the gravitational acceleration negative (-9.8 m/s2) since the helicopter is travelling upwards. F(lift) - F(gravity) = ma F(lift) - (5400kgx(-9.8m/s2)) = (5400kg)(2.17 m/s2) F(lift) = 11718-52920 N F(lift) = -41202 N Shouldnt the lift force acting upon the propellers by positive?