Question Number 23381 by Tinkutara last updated on 29/Oct/17
$$\mathrm{A}\:\mathrm{women}\:\mathrm{swimming}\:\mathrm{upstream}\:\mathrm{is}\:\mathrm{not} \\ $$$$\mathrm{moving}\:\mathrm{with}\:\mathrm{respect}\:\mathrm{to}\:\mathrm{the}\:\mathrm{ground}.\:\mathrm{Is} \\ $$$$\mathrm{she}\:\mathrm{doing}\:\mathrm{any}\:\mathrm{work},\:\mathrm{if}\:\mathrm{she}\:\mathrm{stops} \\ $$$$\mathrm{swimming}\:\mathrm{and}\:\mathrm{merely}\:\mathrm{floats}\:\mathrm{is}\:\mathrm{work} \\ $$$$\mathrm{done}\:\mathrm{on}\:\mathrm{her}? \\ $$
Answered by ajfour last updated on 29/Oct/17
$${Unless}\:{the}\:{sum}\:{of}\:{kinetic}\:{and} \\ $$$${potential}\:{energy}\:{changes},\:{no} \\ $$$${work}\:{is}\:{done}.\:{So},\:{No}\:{for}\:{both}\: \\ $$$${cases};\:{for}\:{the}\:{first}\:{displacement} \\ $$$${is}\:{zero}\:\left({she}\:{resists}\:{motion}\:{of}\right. \\ $$$${flow}\:{as}\:{much}\:{as}\:{she}\:{contibutes} \\ $$$$\left.{to}\:{it}\right).\:{In}\:{the}\:{second}\:{there}\:{is}\:{no} \\ $$$${force}\:{to}\:{imcrease}\:{her}\:{kinetic} \\ $$$${energy}. \\ $$
Commented by Tinkutara last updated on 30/Oct/17
$$\mathrm{Thank}\:\mathrm{you}\:\mathrm{very}\:\mathrm{much}\:\mathrm{Sir}! \\ $$