A) 30 sec
B) 15 sec
C) 10 sec
D) 5 sec
Correct Answer: A
Solution :
If a body starts from rest with acceleration \[\alpha \] and then retards with retardation \[\beta \] and comes to rest. The total time taken for this journey is t and distance covered is S then\[S=\frac{1}{2}\frac{\alpha \beta {{t}^{2}}}{(\alpha +\beta )}=\frac{1}{2}\frac{5\times 10}{(5+10)}\times {{t}^{2}}\] Þ \[1500=\frac{1}{2}\frac{5\times 10}{(5+10)}\times {{t}^{2}}\] \[\Rightarrow \ \ t=30\sec \].
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