The force applied to a cart is 10.5N and the cart moves to the right with a constant velocity. What is the magnitude and direction of the frictional force.

In a previous question where friction was negligible, I determined the mass of the cart was 3.23kg. Do I use that to determine the magnitude of the frictional force in this question? Also, I know since the cart is moving to the right, the frictional force is directed to the left, correct?

Question

The force applied to a cart is 10.5N and the cart moves to the right with a constant velocity. What is the magnitude and direction of the frictional force.

In a previous question where friction was negligible, I determined the mass of the cart was 3.23kg. Do I use that to determine the magnitude of the frictional force in this question? Also, I know since the cart is moving to the right, the frictional force is directed to the left, correct?

amistre64 · Answer

friction is opposite yes


if this a a part of some broader question than i would assume previous results are applicable as well.

theoreo · Answer

I think I have the answer to this, but it doesn't seem right to me. Can somebody verify my work here?

Since velocity is constant, acceleration is zero so F_(net) is zero as well.

$$F_(net) = F_(applied) - F_(friction)$$ so $$ 0= 10.5N - F_(friction)$$

$$F_(friction) = 10.5N$$ directed to the left.

amistre64 · Answer

ill defer to others :)

theoreo · Answer

Ok, thanks for looking in anyway.

amistre64 · Answer

net=0 tends to be when there is no motion, or rather when the threshold is just being reached right?

theoreo · Answer

Yes. So it being zero while an object is in motion really only works when friction is small enough to be negligible right? I had a feeling I'd solved this too simply.

amistre64 · Answer

have you covered an formula like:$$F_k=\mu_k\vec n$$

theoreo · Answer

Yeah, but it was really quick, and my professor has a tendency to be unclear. I'll try to look up a better explanation.

amistre64 · Answer

i see the net zero explanations on the google ...

amistre64 · Answer

google books has a similar question

amistre64 · Answer

http://books.google.com/books?id=GjkvDKvZVrYC&pg=PA106&lpg=PA106&dq=The+force+applied+to+a+cart+is+10.5N+and+the+cart+moves+to+the+right+with+a+constant+velocity&source=bl&ots=uSQ2-QOOgj&sig=jUgNG-l6NLKk7FMRyJosi6cJlj8&hl=en&sa=X&ei=NAk7VIqSItGvyAS01oL4CA&ved=0CFwQ6AEwCA#v=onepage&q&f=false

theoreo · Answer

Oh yeah, this book was written by some of the physics department at my college. It's the same stuff.

amistre64 · Answer

:)  too bad a cant find my old textbooks .... packed away someplace im sure.

amistre64 · Answer

http://www.physicsclassroom.com/class/newtlaws/Lesson-3/Finding-Individual-Forces there are some practice problems similar to this and they follow along the net0 process as well.

mstoldegon · Answer

The question implies that the force is constant, and we shall assume that the cart is on a level surface (that is, the surface is perpendicular to the force of gravity so that no additional force  - negative or positive - is being applied by gravity). If so, and there is no acceleration (as stated), the 10.5N force must be perfectly balanced by all remaining (opposing) forces. As friction of the cart is the only force mentioned, it will be assumed to be the only force opposing the 10.5N force moving the cart to the right.
   Answer: The total magnitude of the friction (bearings, wheel/tire material, surface structure, etc.) is 10.5N and the direction of the force of friction is to the left (exactly 180 degrees to the 10.5N force of motion).
   Hope this helps.