Yellow beautiful souls!!
I am back after about a year and I know no one care but I’m just excited okay. I am going to stop talking and summon the infamous, good hearted, intellectual being @MITer94 to this thread ( gives @MITer94 a virtual hug). Can you please help me with this physics question?
@kunkunta LOL
Is there more than one answer? I think B and D are both correct
When did I become infamous? 
Anyway, I am not and never was a physics major, though shouldn’t it be 200 N (by Newton’s third law)?
I know that B is definitely correct. I do not know if C is 100% correct because there may be work being done on the block or other nonconservative forces.
@MITer94 is right again! The third-law reaction to the 200 N force you applied will always be an equal and opposite 200 N acting on you, regardless of whether the box accelerates or remains at rest.
Whether the 200 N force you exert causes the box to accelerate will depend on if there are other forces also acting on the box.
And whether you accelerate as a result of the 200 N force the box exerts on you will depend on if there are other forces acting on you.
But in all of those cases, Newton’s third law will still be obeyed.
@Monkey288195 I thought so too! @MITer94 @pckeller thank you! But then how can there ever be an external force applied if every force cancels out? How can there be changes? Newton’s first law states that an object in motion will stay in motion and an object at rest will stay that way unless an external/force acts on it. And there won’t be a net force if everything cancels out according to Newton’s third law. Can you please elaborate further? Much appreciated
You have stumbled into a very common misunderstanding, easy to fall into. Let’s see what we can do:
An object accelerates if it experiences an unbalanced force. Clearly, that can happen because objects do in fact accelerate sometimes. But for every force that acts on the object, the object exerts an equal and opposite force. That’s called the “reaction”. So the heart of your question is this: why don’t the reactions cancel the effects of the original force?
The answer is that the reaction force does not cancel the original force because is not acting on the same object as the original force. It’s acting back on the other object, the one that exerted the original force! You will see this more clearly if you make free body diagrams. The action/reaction pair will clearly be acting on two separate objects.
So for example, if you push a block of ice, the block accelerates because of the unbalanced force you exerted on it. It’s true that the block exerted an equal and opposite force, but that force did not act on the block – it acted on you! Depending on what OTHER forces are acting on YOU, you may or may not accelerate as well. But the force the block exerted on YOU can not balance the force that you exerted on the BLOCK.
Hope that helps. And this should probably all be in some other forum…