Tpr physics q 69

[KVS]

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An object is moving on a flat surface and is being acted upon by a net nonzero force F parallel to the surface. The direction of the object's motion must be:

A. The same direction as the direction of F.
B. at a 45 degree angle to the direction of F.
C. Perpendicular to the direction of F
D. Non of the above is necessarily true.


I chose A but the book says the answer is D. The book says that Fnet is always in the direction as the acceleration; it is not always in the same direction as the velocity.

Can some one please explain this to me? Isn't f=ma, so by the book's logic, whatever direction Fnet is in, that will be the direction of the objects motion. Am i completely not understanding this?

 

[DrknoSDN]

An object breaking (reversing direction) would be a good example of why it is not always A.
If an object is moving to the right but the net force is to the left all the parameters of the question can still be true but the direction of motion is opposite to the direction of F.

B and C are hopefully more easily seen as wrong with explanations not being necessary.

 

[Blueprint MCAT Tutor]

DrknoSDN above answered it pretty well, but I've drawn out a picture for you in my science question thread here:

http://forums.studentdoctor.net/threads/specific-science-questions.1053558/

Scroll down to the bottom for it