Question Number 24161 by Tinkutara last updated on 13/Nov/17
$$\mathrm{A}\:\mathrm{door}\:\mathrm{is}\:\mathrm{hinged}\:\mathrm{at}\:\mathrm{one}\:\mathrm{end}\:\mathrm{and}\:\mathrm{is}\:\mathrm{free} \\ $$$$\mathrm{to}\:\mathrm{rotate}\:\mathrm{about}\:\mathrm{a}\:\mathrm{vertical}\:\mathrm{axis}.\:\mathrm{Does}\:\mathrm{its} \\ $$$$\mathrm{weight}\:\mathrm{cause}\:\mathrm{any}\:\mathrm{torque}\:\mathrm{about}\:\mathrm{this} \\ $$$$\mathrm{axis}?\:\mathrm{Give}\:\mathrm{reason}\:\mathrm{for}\:\mathrm{your}\:\mathrm{answer}. \\ $$
Commented by Tinkutara last updated on 13/Nov/17
Answered by physicistG last updated on 13/Nov/17
$${No}\:{torque}\:{is}\:{caused}\:{by}\:{the}\:{weight}\:{against}\:{y} \\ $$
Answered by Physics lover last updated on 14/Nov/17
$${it}\:{is}\:{so}\:{because}\:{there}\:{is}\:{no} \\ $$$${torque}\:{or}\:{its}\:{component}\:{along} \\ $$$${the}\:{fixed}\:{axix}\:{of}\:{the}\:{door}. \\ $$$${the}\:{weight}\:{causes}\:{a}\:{torque}\:{about} \\ $$$${an}\:{axix}\:{which}\:{is}\:{perpendicular} \\ $$$${to}\:{the}\:{fixed}\:{axix}\:{that}'{s}\:{why} \\ $$$${there}\:{is}\:{no}\:{component}\:{about} \\ $$$${the}\:{fixed}\:{axis}. \\ $$
Commented by Tinkutara last updated on 14/Nov/17
$$\mathrm{Thank}\:\mathrm{you}\:\mathrm{very}\:\mathrm{much}\:\mathrm{Sir}! \\ $$