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Question Number 198555 by Tawa11 last updated on 21/Oct/23

Commented by ajfour last updated on 23/Oct/23

$$bothanswerst=\frac{17}{3}sort=5s$$$$iwouldconsiderright.$$

Commented by Tawa11 last updated on 24/Oct/23

$$\mathrm{Thanks}\mathrm{sir}.$$$$\mathrm{I}\mathrm{appreciate}.$$

Answered by Tawa11 last updated on 21/Oct/23

A car 4m long moving at a velocity of 25m/s was beside a lorry 20m long with velocity 19m/s. At t = 0, the distance between them was 10m. How long will it take the car to overtake the lorry. (a) 2s (b) 9s (c) 5s (d) 3s

Commented by mr W last updated on 22/Oct/23

$$answer\left(c\right)$$

Commented by Tawa11 last updated on 23/Oct/23

$$\mathrm{relative}\mathrm{velocity}=25-19=6\mathrm{m}/\mathrm{s}$$$$\mathrm{time}\mathrm{to}\mathrm{cover}10\mathrm{m}$$$$\mathrm{t}=10/6=1.67\mathrm{s}$$$$$$$$\mathrm{for}20\mathrm{m}$$$$\mathrm{relative}\mathrm{velocity}=25-19=6\mathrm{m}/\mathrm{s}$$$$\mathrm{t}=20/6=3.33\mathrm{s}$$$$\mathrm{total}\mathrm{time}$$$$=1.67+3.33$$$$=5\mathrm{s}$$

Commented by Tawa11 last updated on 23/Oct/23

$$\mathrm{Sir},\mathrm{is}\mathrm{this}\mathrm{correct}?$$

Commented by mr W last updated on 23/Oct/23

$$actuallythisshouldbeaneasy$$$$questiontoyou,i^{\prime }dliketoknowwhat$$$$isyourownsolution.$$

Commented by mr W last updated on 23/Oct/23

$$tobeexact,$$$$overtakemeanschangingfromthe$$$$state‘‘behind{something}^{″}tothe$$$$state‘‘infrontofthis{something}^{″}.$$$$thatistosay,forthecarithas$$$$finishedthe‘‘{overtaking}^{″}whenthe$$$$endofthecarhasreachedthefront$$$$ofthelorry.$$$$thatmeansyouhavenotconsidered$$$$thelengthofthecarinyoursolution.$$

Commented by Tawa11 last updated on 23/Oct/23

$$\mathrm{ohh}$$

Commented by Tawa11 last updated on 23/Oct/23

$$\mathrm{Vt}-\mathrm{vt}=\mathrm{L}+\mathrm{d}+\mathrm{l}$$$$\mathrm{t}(25-19)=20+10+4$$$$6\mathrm{t}=34$$$$\mathrm{t}=\frac{34}{6}$$$$\mathrm{t}=5.7\mathrm{s}$$

Commented by Tawa11 last updated on 23/Oct/23

$$\mathrm{Sir},\mathrm{please}\mathrm{check}.$$

Commented by mr W last updated on 23/Oct/23

$$butthisanswerisnotgiven?!$$

Commented by Tawa11 last updated on 23/Oct/23

$$\mathrm{Yes}\mathrm{sir}.$$

Commented by Tawa11 last updated on 23/Oct/23

$$\mathrm{That}\mathrm{is}\mathrm{why}\mathrm{I}\mathrm{posted}\mathrm{the}\mathrm{question}\mathrm{here}.$$

Commented by mr W last updated on 23/Oct/23

$$ihaveguessedthis.otherwiseyou$$$${won}^{\prime }tpostthis‘‘{easy}^{″}question.$$

Commented by mr W last updated on 23/Oct/23

Commented by Tawa11 last updated on 23/Oct/23

$$\mathrm{Show}\mathrm{me}\mathrm{better}\mathrm{way}\mathrm{sir}.$$

Commented by mr W last updated on 23/Oct/23

$$0⩽c<10m$$$$\mathrm{\Delta }t=\frac{4+c+20}{25-19}=\frac{24+c}{6}⩾\frac{24+0}{6}=4s$$$$\mathrm{\Delta }t=\frac{24+c}{6}<\frac{24+10}{6}=5.7s$$$$4s⩽\mathrm{\Delta }t<5.7s$$$$\Rightarrow \left(c\right)istheonlypossiblerightanswer.$$$$with\mathrm{\Delta }t=5:\frac{24+c}{6}=5\Rightarrow c=6m$$$$i.e.thedistancebetweenlorryand$$$$carwas10mandthecarwas6m$$$$behindthelorryindrivingdirection.$$

Commented by Tawa11 last updated on 24/Oct/23

$$\mathrm{Thanks}\mathrm{sir}.$$$$\mathrm{I}\mathrm{appreciate}.$$

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