A) 1.2s
B) 1.3s
C) 1.7 s
D) 2.3 s
Correct Answer: C
Solution :
Effective upwards force \[=310-mg\] \[=310-24\times 9.8=74.8\text{ }N\] \[\therefore \] Upward acceleration \[a=\frac{74.8}{24}=3.12\,m{{s}^{-2}}\] As \[s=ut+\frac{1}{2}a{{t}^{2}}\] \[4.6=0+\frac{1}{2}\times 3.12\times {{t}^{2}}\] Or \[{{t}^{2}}=\frac{4.6}{1.56}=2.95\] \[\therefore \] \[t=\sqrt{2.95}=1.7\,s\]
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