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I only see one force so I figure it should be a non-zero net force. Every exampl

ID: 2298336 • Letter: I

Question

I only see one force so I figure it should be a non-zero net force. Every example I found online indicated that to have a net force of zero there should be one counteracting it,

A small, solid cylinder with mass 2 kg and radius 3 cm starts from rest and rotates without friction about an axis through its center of mass. The rotation axis is fixed so that the center of mass of the cylinder does not move as the cylinder rotates. A string is wrapped around the circumference of the cylinder and is pulled using a constant force F=5 N. Which of the following statements is true?

Explanation / Answer

Although the string is applying torque to the cylinder, just look at 2nd law to know that the net force must be zero. The cylinder's center of mass isn't accelerating, so we treat it as if the cylinder isn't accelerating, and therefore the net force must be zero.