Newton's Laws and finding magnitude

[physics_10]

An object of mass 1.25 kg on a flat surface has two forces acting on it, F1 and F2 in the horizantal direction. F1 acts in the positive direction, F2 acts in the negative direction. The magnitude of F1 is 26.75 N. The object moves strictly along the horizontal x-axis, which we choose as positive to the right. Find the magnitude of F2 if the object has a horizontal acceleration of 9.3 m/s2.



No clue where to start. Any help would be great !

 

[tiny-tim]

hi physics_10!

use good ol' Newton's second law … F_total = ma …

what do you get? ​

 

[physics_10]

11.63 N. so that's it? I don't need to do anything with F1?

 

[tiny-tim]

(try using the X₂ icon just above the Reply box )

11.63 N. so that's it?

no, that would be the value of F₂ if F₂ was the total force

try again ​

 

[physics_10]

Is it F1-F2..
so 26.72-11.63 = 15.09 N?

 

[tiny-tim]

Is it F1-F2..
so 26.72-11.63 = 15.09 N?

that's right!

F_total = F₁ + F₂ = 26.72-11.63, and that has to equal ma.

(but is it 26.72 or 26.75?)