Physics Help Forum Need Help with this Friction Problem

 Kinematics and Dynamics Kinematics and Dynamics Physics Help Forum

 May 6th 2013, 08:39 PM #1 Junior Member   Join Date: May 2013 Posts: 1 Need Help with this Friction Problem Hi, My colleague and I are having problems with this question. We are in contentions with option B and D. Option B Since the cart is being pushed, the wheels rotate in an anticlockwise direction and thus the friction should be opposite to the wheel's rotation. However, when a force is not applied, the cart slows down and thus friction should be to the right. Option D Since the cart is being pushed and no driving force exerted by the wheel, the friction is similar to that of a box sliding across a floor. The wheels help to reduce friction in this case. It would be great to hear your views. Jeevan
 May 7th 2013, 01:41 PM #2 Physics Team     Join Date: Jun 2010 Location: Morristown, NJ USA Posts: 2,347 Since you have posted only a portion of the problem it's difficult to understand what's going on. However, regarding a rolling wheel on a floor - consider that if friction = 0 the wheel would not rotate, but would just slide (like a car on ice). So if the wheel is rotating there must be friction between the floor and the wheel that causes it to rotate, and the direction of this force on the wheel is in the direction of rotation. The friction force must be great enough to overcome the rotational inertia of the wheel and any friction in the bearings of the wheel.

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