A) 20 m
B) 40 m
C) 60 m
D) 80 m
Correct Answer: D
Solution :
| [d] The braking retardation will remain same and assumed to be constant, let it be a. |
| From equation of motion,\[{{v}^{2}}={{u}^{2}}+2as\] |
| 1st case \[0={{\left( 60\times \frac{5}{18} \right)}^{2}}-2a\times {{s}_{1}}\] |
| \[\Rightarrow \]\[{{s}_{1}}=\frac{{{(60\times 5/18)}^{2}}}{2a}\] |
| 2nd case \[0={{\left( 120\times \frac{5}{18} \right)}^{2}}-2a\times {{s}_{2}}\] |
| \[\Rightarrow \]\[{{s}_{2}}=\frac{{{(120\times 5/18)}^{2}}}{2a}\] |
| \[\therefore \]\[\frac{{{s}_{1}}}{{{s}_{2}}}=\frac{1}{4}\] |
| \[\Rightarrow \]\[{{s}_{2}}=4{{s}_{1}}\] |
| \[=4\times 20=80\,m\] |
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