which formula can i use to find the weight of a 13 lb object?

The weight of a 13 lb. object is 13 pounds. That's what "13-pound object" means.

We express WEIGHT in newtons.

We also express FORCE in newtons.

Which has to tell you weight of an object is actually its force due to the acceleration (in this case acceleration of the Earth, g).

Which would then tell you there is no difference in the formulas.

On another note, if both F AND W are equal to m*g, that's also gotta tell you they're the same thing (for now).

Apart from that, weight (just like force, obviously, is ALWAYS in newtons. So no, it isn't 13 lbs).

F(or W) = 13 lb * 9.8 m/s^2

Now, I don't know if you caught this in class, but something has to be converted here. And that will obviously be the mass of the object, to kilograms.

13 lb = 5.9 kg.

Now the weight of the object is:

W = (5.9 kg) * (9.8 m/s^2) = 57.82 N.

:)

Reread your assignment; this time pay attention to the definition of weight and mass. One learns physics by starting with the definitions; not by memorizing formulas that without the physics you'll have no clue: is it F = mg or W = mg.

You are asking that question because you don't know the physics...the definitions in this case.