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mathslover
 3 years ago
A 2m wide car is moving uniformly with a speed of 8m/s along the edge of a straight horizontal road. A pedestriun starts to cross a road with a speed "v" when the car is 12 m away from him. The minimum value of v for the pedestrian to cross the road safety is ?
mathslover
 3 years ago
A 2m wide car is moving uniformly with a speed of 8m/s along the edge of a straight horizontal road. A pedestriun starts to cross a road with a speed "v" when the car is 12 m away from him. The minimum value of v for the pedestrian to cross the road safety is ?

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ash2326
 3 years ago
Best ResponseYou've already chosen the best response.0There can be two cases, either the man crosses the road before the car reach him or he crosses it after the car has crossed

mathslover
 3 years ago
Best ResponseYou've already chosen the best response.0well if we take the man to reach more safely there is that is the first case

ash2326
 3 years ago
Best ResponseYou've already chosen the best response.0see the diagramdw:1361020408653:dw Time taken for car to reach the man, \[12 m\div 8 m/s= 1.5 seconds\] In this time the man should cover the 2 meter distance, fairly simple now Can you find v?

DLS
 3 years ago
Best ResponseYou've already chosen the best response.1dw:1361020539994:dw @ash2326 just trying..i dont think there will be 2 cases,he should move making an angle theta with the axis not straight..

mathslover
 3 years ago
Best ResponseYou've already chosen the best response.0yeah @DLS has a point\

ash2326
 3 years ago
Best ResponseYou've already chosen the best response.0But we need to find the minimum V for that, he has to walk straight

mathslover
 3 years ago
Best ResponseYou've already chosen the best response.0the man will make an angle theta first we have to find the componenets ( x and y ) and then solve for theta

ash2326
 3 years ago
Best ResponseYou've already chosen the best response.0dw:1361020702285:dw We aren't given D, we can't find angle without it

mathslover
 3 years ago
Best ResponseYou've already chosen the best response.0dw:1361020857966:dw

DLS
 3 years ago
Best ResponseYou've already chosen the best response.1\[v=\frac{d}{t} \] \[BC=2cosec \theta\] \[t_{bus}=t_{boy} \] \[\frac{4+2\cot \theta}{8}=\frac{8}{v}=2\sin \theta+\cos \theta \] \[v=\frac{8}{2\sin \theta+\cos \theta}\] for v to be minimummmmmmmmmmm \[\frac{dv}{d \theta}=0\] \[\frac{d8(2 \sin \theta+\cos \theta)^1}{d \theta}=0\]

DLS
 3 years ago
Best ResponseYou've already chosen the best response.1sorry i took the distance 4m correct that value..

DLS
 3 years ago
Best ResponseYou've already chosen the best response.1if my solution is close enough

mathslover
 3 years ago
Best ResponseYou've already chosen the best response.0how r those angles : 2 cot theta and 2 cosec theta ?

DLS
 3 years ago
Best ResponseYou've already chosen the best response.1\[\LARGE \frac{12+2\cot \theta}{8}=\frac{8}{v}=\frac{6+\cot \theta}{4}\]

ash2326
 3 years ago
Best ResponseYou've already chosen the best response.0How do you have 8/v? man isn't travelling 8 meters

DLS
 3 years ago
Best ResponseYou've already chosen the best response.1@ash2326 I equated the times.. Tbus=Tboy

ash2326
 3 years ago
Best ResponseYou've already chosen the best response.0I know that but man has to travel \[\sqrt{2^2+(2\cot \theta)^2}\] so it should be \[\frac{\sqrt{2^2+(2\cot \theta)^2}}{v}\]

DLS
 3 years ago
Best ResponseYou've already chosen the best response.1yeah i got ur query,hold on

DLS
 3 years ago
Best ResponseYou've already chosen the best response.1i took that 12+2cot theta that is the total distance he has to travel i guess distance is scalar :o so why are u adding it vectorally? im getting confused too :S

ash2326
 3 years ago
Best ResponseYou've already chosen the best response.0I solved this, there is no global minima for v. We need to revisit the problem

mathslover
 3 years ago
Best ResponseYou've already chosen the best response.0got to go now,,,... sorry but please post your opinions

ash2326
 3 years ago
Best ResponseYou've already chosen the best response.0@DLS the man is travelling with an angle, his speed is v I just found the hypotenuse distance

DLS
 3 years ago
Best ResponseYou've already chosen the best response.1i thought that was 2 cosec theta :O

ash2326
 3 years ago
Best ResponseYou've already chosen the best response.0Yes, if you solve the square root, you will get 2 cosec theta

ash2326
 3 years ago
Best ResponseYou've already chosen the best response.0I'm not convinced about the car travelling an extra distance 2 cot theta

ash2326
 3 years ago
Best ResponseYou've already chosen the best response.0@mathslover do you have answer for this?

DLS
 3 years ago
Best ResponseYou've already chosen the best response.1Just do the whole thing for him :P From the beginning :D

mathslover
 3 years ago
Best ResponseYou've already chosen the best response.0yep  4/3  ans..

anonymous
 3 years ago
Best ResponseYou've already chosen the best response.0doing all that other crap!! :P.. good thing you put up the answer!!

mathslover
 3 years ago
Best ResponseYou've already chosen the best response.0@Mashy you cn put up your soln... I posted it becz ash wnted to check the ans... Please post your soln

anonymous
 3 years ago
Best ResponseYou've already chosen the best response.04/3 is the simple method.. of going straight :O..

anonymous
 3 years ago
Best ResponseYou've already chosen the best response.0before i can start i need to know the in physics what is the start point for all formula is = to ? or 0.00 or what the name of all start point plz? start point =

ash2326
 3 years ago
Best ResponseYou've already chosen the best response.0@mathslover Use my first post, I had told you for minimum it has to be straight

mathslover
 3 years ago
Best ResponseYou've already chosen the best response.0DLS can you tell me how you got 2 cot theta there ?

mathslover
 3 years ago
Best ResponseYou've already chosen the best response.0dw:1361184323999:dw ok :)

DLS
 3 years ago
Best ResponseYou've already chosen the best response.1isnt the sol clear? they are taking for it to be going straight

mathslover
 3 years ago
Best ResponseYou've already chosen the best response.0But I am trying to do for the angle theta... please tell how you got 2 cot theta there

DLS
 3 years ago
Best ResponseYou've already chosen the best response.1dw:1361185375230:dw AC=2 cot theta

DLS
 3 years ago
Best ResponseYou've already chosen the best response.1\[\LARGE \cot \theta=\frac{1}{\tan \theta}\]

DLS
 3 years ago
Best ResponseYou've already chosen the best response.1\[\LARGE \cot \theta=\frac{AC}{2}\]

mathslover
 3 years ago
Best ResponseYou've already chosen the best response.0OH got it thanks a lot
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