A) 72
B) 92.5
C) 102.6
D) 129.6
Correct Answer: D
Solution :
Key Idea: When automobile stops, final velocity is zero. From equation of motion \[{{v}^{2}}={{u}^{2}}-2as\] where\[u\] is initial velocity, a is acceleration and s is displacement. Given,\[u=50\,km/h,\,v=0,s=40\,m\] \[\therefore \] \[a=\frac{{{u}^{2}}}{2s}=\frac{{{\left( 50\times \frac{5}{18} \right)}^{2}}}{2\times 40},\] when \[u'=90\,km/h,\,a=\frac{{{\left( 50\times \frac{5}{18} \right)}^{2}}}{2\times 40},v=0\] \[s=\frac{u{{'}^{2}}}{2a}\] \[\Rightarrow \] \[s=\frac{{{\left( 90\times \frac{5}{18} \right)}^{2}}\times 2\times 40}{2\times {{\left( 50\times \frac{5}{18} \right)}^{2}}}\] In metre \[s=129.6\,m\]
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