It increases confidence because the more times you conduct the same experiment over and over should either prove your hypothesis right and wrong and eliminate any random occurrences that might affect your results.
In Grams it would be 509.85 (1 N=101.97g)
Well to find instantaneous speed, you basically make the time frame really short, so basically measure the distance the object moves within a small amount of time(0.1 seconds or something). The smaller the time, the more accurate the instantaneous speed is.
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The uncharged body will gain electrons from the charged body. Giving the uncharged body a shock.