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A driver of a car travelling …

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A driver of a car travelling at 52kmp/h applies the brake and accelerayed unniformly in the opposite dirrection.The car stops in 5 sec's. Another driver going at 3kmp/h in another car applies his brake slowly and stops in 10 sec's on the same graph paper plot the speed vs time graph for the 2 cars. Which of the 2 cars travel farther after the breaks are applied?
  • 1 answers

Sia ? 4 years, 8 months ago


As given in the figure below AB (in red line) and CD(in red line) are the Speed-time graph for given two cars with initial speeds 52kmh-1 and 3 km h-1 respectively.
Distance Travelled by first car before coming to rest =Area of {tex}\triangle{/tex}OAB
= ({tex}\frac{1}{2}{/tex})  {tex}\times{/tex} OB {tex}\times{/tex} OA
= ({tex}\frac{1}{2}{/tex}{tex}\times{/tex} 5s {tex}\times{/tex} 52 kmh-1
= ({tex}\frac{1}{2}{/tex}{tex}\times{/tex} 5 {tex}\times{/tex} (52  {tex}\times{/tex} 1000)/3600)m
= ({tex}\frac{1}{2}{/tex}) {tex}\times{/tex} 5 {tex}\times{/tex} ({tex}\frac{130}{9}{/tex} )m
= {tex}\frac{325}{9}{/tex}
= 36.11 m
Distance Travelled by second car before coming to rest =Area of {tex}\triangle{/tex}OCD
= ({tex}\frac{1}{2}{/tex}{tex}\times{/tex} OD {tex}\times{/tex} OA
= ({tex}\frac{1}{2}{/tex}{tex}\times{/tex} 10 s {tex}\times{/tex} 3 kmh-1 
=({tex}\frac{1}{2}{/tex}{tex}\times{/tex} 10 {tex}\times{/tex} ({tex}\frac{3 \times 1000}{3600}{/tex}) m 
= ({tex}\frac{1}{2}{/tex}{tex}\times{/tex} 10 {tex}\times{/tex} ({tex}\frac{5}{6}{/tex}) m
= 5 {tex}\times{/tex}({tex}\frac{5}{6}{/tex}) m 
= {tex}\frac{25}{6}{/tex} m
= 4.16 m
{tex}\therefore{/tex} Clearly the first car will travel farther(36.11 m)than the first car(4.16 m).

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