Question Number 47801 by Rio Michael last updated on 14/Nov/18
$${An}\:{object}\:{starts}\:{from}\:{rest}\:{and}\:{moves}\:{with}\:{a}\:{velocity}\:{of}\: \\ $$$$\left(\mathrm{3}{i}+\mathrm{4}{j}\right){ms}^{−\mathrm{1}} .\:{It}\:{covers}\:{a}\:{distance}\:{of}\:\mathrm{400}{km}.{Find}\: \\ $$$$\left.{a}\right)\:{its}\:{acceleration} \\ $$$$\left.{b}\right)\:{the}\:{time}\:{taken}\:{to}\:{cover}\:{the}\:{distance}\:\mathrm{400}{km}. \\ $$
Answered by mr W last updated on 15/Nov/18
$${velocity}=\sqrt{\mathrm{3}^{\mathrm{2}} +\mathrm{4}^{\mathrm{2}} }=\mathrm{5}\:{m}/{s}={constant} \\ $$$$\left.{a}\right)\:{accerleration}\:{is}\:{zero} \\ $$$$\left.{b}\right)\:{time}=\mathrm{400}/\mathrm{5}=\mathrm{80}\:{seconds} \\ $$$${if}\:{you}\:{really}\:{mean}\:\mathrm{400}\:{km},\:{then} \\ $$$${time}=\mathrm{400000}/\mathrm{5}=\mathrm{80000}\:{s}=\mathrm{22}.\mathrm{2}\:{h}\approx\:\mathrm{1}\:{day} \\ $$