# Is my teacher wrong? Problem dealing with forces.

1. Jan 14, 2012

### Kinermatics

1. The problem statement, all variables and given/known data
Problem is in the picture

2. Relevant equations
The teacher told us the
Fnetx = 20N - Fx (Fx is 0)
Fnety = Fy - 50N (Fy = +25N)

3. The attempt at a solution
My answer was 32N. But my teacher said the answer was C. which was 77.5N. He got it because Fnety = 75N for him. But that to me doesn't make sense since the Fy and 50N are pointing in opposite directions, won't Fnety be = -25N?

#### Attached Files:

• ###### forces.jpg
File size:
42.9 KB
Views:
91
2. Jan 14, 2012

### Kinermatics

Oh nvm i think i got it. I think he meant to put that:
25N = Fy - 50 huh? Darn and to think i could prove a teacher wrong ;"D

3. Jan 15, 2012

### Redbelly98

Staff Emeritus
Welcome to PF.
Glad it worked out finally. The key here was to think carefully about which sign (+ or -) goes with each force -- including Fnety, which we know is + because the object accelerates in the +y direction.
It pays to be careful -- those forces in parentheses should read (Fnetx is 0) and (Fnety = +25N)