How often do the earth's magnetic poles switch?

A100 kg running back runs at 5m/s into a stationary linebacker. it takes 0.5 for the running back to be completely stopped

Along the line connecting the two charges, at what distance from the charge q1 is the total electric field from the two charges zero? express your answer in terms of some or all of the variables s, q1, q2 and k =14ï€ïµ0. if your answer is difficult to enter, consider simplifying it, as it can be made relatively simple with some work.

Hunter’s velocity was 4.5 m/s. at the end of his race, his velocity was the same. which best describes his movement? his movement stopped. his acceleration is zero. his time was constant. his acceleration was positive.