chocolatelover

Hello everyone,

Could someone please help me with this or give me a hint?

If the mass of the object is m, what is the minimum force F needed to raise the object? Use Newton’s 2nd law.

My attempt:

F=ma

Thank you very much

arbolis

I give you a big hint. An object has a mass $\displaystyle m$, so it has a weight $\displaystyle m\cdot g$.
To raise it, the total force in the direction of the weight force must be in the upward direction. Do you catch what I'm saying?

__________________
Isaac
If the problem is too hard just let the Universe solve it.

chocolatelover

Thank you very much

So, since the force of the weight=mg and when you raise the total force it is in the upward direction, when you raise the minimum force it would be in the negative direction, right?

Thank you

arbolis

Yes. You will get something like : The minimum force must be greater than ...$\displaystyle N$.
In fact, if you maintain the minimal force required to rise the body in the air applied on the body, it will rise up in the air faster and faster.

And about The answer is no.
Chose a referential system in which the positive direction is upward and the negative direction is downward. The weight (which is a force) has its direction downward while the minimum force required to raise the object must be upward, otherwise the sum of the forces will point downward (that is toward the center of the Earth) and the object would not move at all.

EDIT : If you don't mind, once you get the answer post it here so that we can check it out.

__________________
Isaac
If the problem is too hard just let the Universe solve it.

chocolatelover

Is it "The minimum force must be F=mg"?

Thank you very much

or is it "the maximum force-minimum force=0" or "the minimum force=0-maximum force"

arbolis

Almost. If you apply a force equal to the weight but in the opposite direction, the object will not move (it will move at a constant velocity in fact. But as it was with an initial velocity equal to $\displaystyle \frac{0m}{s}$, it will conserve this velocity). So the answer should be "the minimal force to raise an object of mass m must be greater than $\displaystyle mg$".
Anyway I think you got the idea, so congratulations!

__________________
Isaac
If the problem is too hard just let the Universe solve it.

chocolatelover

Thank you very much

Regards