For this exercise, imagine a large positive charge +Q fixed at some location in

Question

For this exercise, imagine a large positive charge +Q fixed at some location in otherwise empty space, far from all other charges. A positive test charge of smaller magnitude +q is launched directly towards the fixed charge. Of course, as the test charge gets closer, the repulsive force exerted on it by the fixed charge slows it down. Your job is to explain why the test charge slows down, but in terms of electric potential and EPE, rather than in terms of fields or forces.




In particular:

•explain how the electrical potential encountered by the test charge changes as it gets closer to the fixed charge, and why

•explain how the EPE of the test charge changes as it gets closer to the fixed charge, and why




On that basis, explain why the test charge +q slows down as it approaches the fixed charge +Q.




Your response shouldn't mention either fields or forces

NOTE:THIS IS THE ANSWER I TURNED IN:
"The test charge starts out with full kinetic energy, and as the test charge gets closer to the +Q, the kinetic energy is being transferred into electric potential energy. This conversion expresses that KE is decreasing until the test charge reaches its max distance
"
THE INSTRUCTOR SAID:
"This is in essence the correct explanation in terms of energy. If you can prove that the EPE of q rises due to getting closer to Q, then you'll have a complete explanation. I'm not sure what you mean by "max distance" - please use whole words, for one thing, but if the test charge is getting close to the fixed charge, how can there be a maximum distance?"

Explanation / Answer

As the test charge is projected towards large positive charge Q with full kinetic energy, its petential energy at the begining is zero. Total mechanical energy=KE+PE at the begining total energy is only KE. -------------------------------------------------------------------------------------------------------- Law of conservation energy states that total energy of the object remains constant as the object moves, provided that net work done by external nonconservative force is zero.   PE increse because work done against repulsion (conservative force) is increasing as test charge approaches fixed large positive charge. To balance total energy, KE slowly decrease. so the test +q is is slowing down. On reaching a minimum distance total energy is only PE. EPE=kQq / r where r is minimu distance of test charge (+q) from fixed large charge(Q)

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