An object's motion changes
A.
only when a nonzero net force is applied to the object.

B.
only if the object is at rest when a force acts upon it.

C.
when the forces acting on the object remain balanced.

D.
all of these

Question

An object's motion changes
  A. 
only when a nonzero net force is applied to the object.

  B. 
only if the object is at rest when a force acts upon it.

  C. 
when the forces acting on the object remain balanced.

  D. 
all of these

anonymous · Answer

@SolomonZelman

anonymous · Answer

@ags2658

anonymous · Answer

c

solomonzelman · Answer

I don't think so...

anonymous · Answer

Okay. C can be eliminated, first of all. When all of the forces on an object are BALANCED, the object either:
Moves at a constant velocity (NO Acceleration)
OR
Doesn't move at all (Stays still, such as a book on a table)
Therefore, C is not the right answer.

anonymous · Answer

D can be eliminated, since ''all of these'' are not right. One choice was just eliminated.

anonymous · Answer

yeah then i think a

anonymous · Answer

i mean b

solomonzelman · Answer

Well, if the object is at rest
(in whatever reference frame that you are in)
and (with the same raference frame) you apply a
none zero force,

THEN,

I would say that the motion of that
object does change, isn't that so?

solomonzelman · Answer

But, to say that b is the definition of the object changing motion ?
That would be too ignorant.

anonymous · Answer

wait so a or b im confused

anonymous · Answer

Well, for B, imagine a cart is moving at a CONSTANT VELOCITY. It is not accelerating (therefore no CHANGE in motion). Then, a force is applied to it, making it accelerate. The object was NOT at rest. It was moving, and it still had a CHANGE in motion (acceleration). Therefore, B is not right.
A is the only answer choice left. A net force is calculated by subtracting the smaller force from the bigger force. If that difference ends up being a nonzero number (a number other than 0), this means that an UNBALANCED force is acting on the object. That is why A is correct.  :D

anonymous · Answer

oh ok thx
@ags2658  can yougive soloman a medal

solomonzelman · Answer

I don't need

solomonzelman · Answer

my prof already looks suspicious... and not here for that:)

anonymous · Answer

Sure! He earned it! Do you still want it?

anonymous · Answer

ill take it if he doesnt want lol

solomonzelman · Answer

(((Assuming we are taking about a linear motion, but a velocity could be constant with a centripetal acceleration.... )))

solomonzelman · Answer

(for example)

anonymous · Answer

1 more guys plz hellp

anonymous · Answer

You are correct, but this is a more simplistic problem. Unless you think the answer is another letter, lol.  :D

anonymous · Answer

I understand that you are naming gaps in the answer, though.  ^^

solomonzelman · Answer

An object changes motion?
Means that it it's velocity changes.

When a net force is not zero, the object is accelerating, and thus changing velocity. So wouldn't this mean "changes motion"?
(So A)

If the object is at rest and a force acts upon it, it might not necessarily move. Force of friction might stop it, for example. Also, we didn't say that the force is not 0, so the answer isn't B.