A) \[70\text{ }km{{h}^{1}}\]
B) \[70.7\text{ }km{{h}^{1}}\]
C) \[65\text{ }km{{h}^{1}}\]
D) \[75\text{ }km{{h}^{1}}\]
Correct Answer: B
Solution :
| [b] From, |
| \[{{v}^{2}}{{u}^{2}}=2as\] |
| \[\frac{{{80}^{2}}-\,{{60}^{2}}}{2a}\,=s\] |
| \[s=\,\frac{6400\,-3600}{2a}\,\,=\,\frac{1400}{a}\] |
| The middle point of the train is to cover a distance |
| \[\frac{s}{2}=\,\frac{700}{a}\] |
| From, \[{{v}^{2}}{{u}^{2}}=2as\] |
| \[{{v}^{2}}-{{60}^{2}}=2a\times \,\frac{700}{a}\] |
| = 1400 |
| \[{{v}^{2}}=1400+3600\] |
| \[v=\sqrt{5000}\] |
| \[=70.7\text{ }km{{h}^{1}}\] |
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