Force and Work

[Riddl3r]

1. The problem statement, all variables and given/known data

Our teacher made an unconvincing argument based on this example:
If a horizontal force of 15 N were a applied to a 2 kg block, and the work done was 20 J, what distance did the object move?

2. The attempt at a solution
Using W=F*d the teacher solved this: 20 J=15 N*x -> x=4/3 m.
This implied that if I applied 15 N to an object of any mass and did 20 J of work, the distance I could move the object is always the same. There seems to be something fundamentally wrong with this statement. But I'm not seeing what it is, I know it's there - I'm think that somehow I need to do something with the weight of the object. I mean if it were to be realistic I would have to calculate friction and gravity too...

Can somebody please tell me what I missed out?

[dirk_mec1]

2. The attempt at a solution
Using W=F*d the teacher solved this: 20 J=15 N*x -> x=4/3 m.
This implied that if I applied 15 N to an object of any mass and did 20 J of work, the distance I could move the object is always the same.

That's correct.


There seems to be something fundamentally wrong with this statement. But I'm not seeing what it is, I know it's there - I'm think that somehow I need to do something with the weight of the object. I mean if it were to be realistic I would have to calculate friction and gravity too...

Can somebody please tell me what I missed out?
Usually we neglect friction and the gravity doesn't play a role here because this is a horizontal motion.

[Kushal]

it's more like a resultant force of 15N which moves the body 4/3 m when 20 J of work is done. the 15 N resultant force may include the force you apply - any resistive forces for example.

[Riddl3r]

Oh I see what you're saying, I guess my teacher didn't convey that point very well^^