A) decreases by 11 percent
B) increases by 11 percent
C) decreases by 90 percent
D) increases by 90 percent
Correct Answer: C
Solution :
Suppose \[{{t}_{0}}\] be the time to reach maximum height in the absence of air resistance, then from the relation \[{{t}_{0}}=\frac{u\,\sin \,\alpha }{g}\] ??(1) when a is retardation caused by air resistance, then total retardation will be \[g+a\] \[{{t}_{1}}=\frac{u\sin \alpha }{g+a}=\frac{u\sin \alpha }{g+\left( \frac{1}{10} \right)g}=\frac{10u\,\sin \alpha }{11g}\] ?..(2) Now from equations (1) and (2), we have \[{{t}_{1}}=\frac{10}{11}{{t}_{0}}\] or \[{{t}_{1}}=90%\,{{t}_{0}}\] Time will decrease by 90%.
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