A 391 kg piano slides 3.7 m down a(n) 27° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 7-23). The effective coefficient of kinetic friction is 0.40. Figure 7-23 (a) Calculate the force exerted by the man. 374N (b) Calculate the work done by the man on the piano. -1384J (c) Calculate the work done by the friction force. -5054J (d) Calculate the work done by the force of gravity. 6438J (e) Calculate the net work done on the piano. _____J I got the previous questions correct with the exception of letter "e". This is what I did... WORKnet = Wgravity-Wfriction+Wnormal force in x direction-Work man in x direction My numbers were 6438-5054+6437-1384 = 6437J The problem must be in the way I'm calculating the normal force in the x direction. I used Fn=Fg*sin27*3.7m=6437J Thanks in advance for the help.