Exam was preety good. There was like only like one center mass question, where you could even use the momentum conservation to solve

@Abcd I get (1): i.imgur.com/Pf2N6Xy.jpg

@Mr.Xcoder I think it should be 4th one.

The force $F_2$ contributes to torque in +Z direction.

And there's no contribution by $F_1$ along z axis.

Right?

@Dante Isn't $F_2$ in XY plane?

That's what the question states

Oh, sorry, I was using right hand thumb rule to find out the direction, but angle was obtuse there.

Nvm, your answer is correct.

But I've got a mistake in there as well

What is it?

For $F_2$, $F_{2x}=-F/2$ and $F_{2y}=-F\sqrt 3/2$.

That swaps some signs

I forgot the negative signs

So (4) should be correct indeed.

Oh, but you've still got the right answer I guess. Torque due to $F_2$ (which is along z axis) has to be negative.

Hmm, by applying the right hand rule I see it should be in the positive Oz direction

Angle between r and F is 120

Just checked the key, 1st option it is.

Umm...

If you make r and F co-initial vectors, you will find angle between them is 120

that means I've made 2 mistakes in there

@Dante Not 150?

Both the mistakes cancelled out each other :p

Ah, sorry 150

It's 2 am here, I think I must sleep

;_;

Goodbye @Mr.Xcoder !

Good night, I guess