Question Number 22071 by Tinkutara last updated on 10/Oct/17
$$\mathrm{STATEMENT}-\mathrm{1}\::\:\mathrm{If}\:\mathrm{an}\:\mathrm{object}\:\mathrm{is}\:\mathrm{at} \\ $$$$\mathrm{rest}\:\mathrm{then}\:\mathrm{there}\:\mathrm{should}\:\mathrm{not}\:\mathrm{be}\:\mathrm{any}\:\mathrm{friction} \\ $$$$\mathrm{on}\:\mathrm{it}. \\ $$$$\mathrm{STATEMENT}-\mathrm{2}\::\:\mathrm{If}\:\mathrm{an}\:\mathrm{object}\:\mathrm{is}\:\mathrm{moving} \\ $$$$\mathrm{then}\:\mathrm{the}\:\mathrm{friction}\:\mathrm{acting}\:\mathrm{on}\:\mathrm{it}\:\mathrm{has}\:\mathrm{to}\:\mathrm{be} \\ $$$$\mathrm{kinetic}. \\ $$$$\mathrm{STATEMENT}-\mathrm{3}\::\:\mathrm{If}\:\mathrm{an}\:\mathrm{object}\:\mathrm{is}\:\mathrm{at}\:\mathrm{rest} \\ $$$$\mathrm{then}\:\mathrm{kinetic}\:\mathrm{friction}\:\mathrm{cannot}\:\mathrm{act}\:\mathrm{on}\:\mathrm{it}. \\ $$
Commented by ajfour last updated on 10/Oct/17
$$\:{a}\:{block}\:{not}\:{slipping}\:{and}\:{resting} \\ $$$${on}\:{a}\:{rough}\:{inclined}\:{plane}\:,\:{then} \\ $$$${friction}\:{is}\:{in}\:{action}. \\ $$$$ \\ $$$${a}\:{wheel}\:\:{rolling}\:{without}\:{sliding} \\ $$$${on}\:{a}\:{rough}\:{plain}\:{horizontal}\:{floor}, \\ $$$${no}\:{friction}\:\:{acts}. \\ $$$$ \\ $$$${other}\:{forces}\:{keep}\:{a}\:{the}\:{object} \\ $$$${at}\:{rest}\:{while}\:{some}\:{other}\:{object} \\ $$$${slides}\:{over}\:{it}.\: \\ $$
Commented by Tinkutara last updated on 11/Oct/17
$$\mathrm{3}^{\mathrm{rd}} \:\mathrm{is}\:\mathrm{not}\:\mathrm{clear}.\:\mathrm{Why}\:\mathrm{kinetic}\:\mathrm{friction} \\ $$$$\mathrm{will}\:\mathrm{act}\:\mathrm{on}\:\mathrm{it}\:\mathrm{then}? \\ $$
Commented by ajfour last updated on 11/Oct/17
$${say}\:{a}\:{light}\:{block}\:{slides}\:{on}\:{the}\: \\ $$$${inclined}\:{surface}\:{of}\:{a}\:{heavy} \\ $$$${wedge},\:{the}\:{wedge}\:{remains}\:{at} \\ $$$${rest}\:{but}\:{there}\:{is}\:{kinetic}\:{friction} \\ $$$${between}\:{block}\:{and}\:{wedge}\:{which} \\ $$$${the}\:{wedge}\:{expeeiences}\:{and}\:{it}\:{is} \\ $$$${at}\:{rest}\:{due}\:{to}\:{static}\:{friction}\:{on} \\ $$$${ground}. \\ $$
Commented by Tinkutara last updated on 11/Oct/17
$$\mathrm{Thank}\:\mathrm{you}\:\mathrm{very}\:\mathrm{much}\:\mathrm{Sir}! \\ $$
Answered by ajfour last updated on 10/Oct/17
$$\mathrm{1}−{not}\:{always}\:{true} \\ $$$$\mathrm{2}−{not}\:{always}\:{true} \\ $$$$\mathrm{3}−{not}\:{always}\:{true} \\ $$