Which of the following is an example of a nonconservative force? 1) magnetism 3) friction 4) Both choices \( A \) and \( B \) are valid. 5) Both choices \( A \) and \( C \) are valid.

To determine which of the options represents a nonconservative force, let's first define what a nonconservative force is. A nonconservative force is one where the work done by the force depends on the path taken. In contrast, conservative forces (like gravity and magnetism) have the property that the work done is independent of the path and depends only on the initial and final positions. Now, let's analyze the options: 1) **Magnetism**: This is generally considered a conservative force because the work done by magnetic forces on a charged particle moving in a magnetic field is path-independent. 2) **Friction**: This is a nonconservative force because the work done by friction depends on the path taken. It dissipates energy as heat, which is not recoverable. Now, let's evaluate the choices: - **Choice 1 (magnetism)** is conservative. - **Choice 3 (friction)** is nonconservative. - **Choice 4 (Both choices A and B)** is incorrect because choice A (magnetism) is conservative. - **Choice 5 (Both choices A and C)** is also incorrect because choice A (magnetism) is conservative. Thus, the correct answer is: **3) friction** is an example of a nonconservative force.