Question
When a ruler falls vertically, 5 different persons catch it with different reaction times. ( $g = 9.8\text{ }m{\text{ }s}^{- 2}$ )
A. Person A has reaction time of 0.20 s .
B. Person B has reaction time of 0.22 s.
C. Person C has reaction time of 0.18 s.
D. Person D has reaction time of 0.19 s.
E. Person E has reaction time of 0.21 s.
What is the correct order of the distance travelled by the ruler for each person?
Options
Solution
Sol. [Key Concept: Free fall — reaction time from s = ½gt²] → There will be large distance for large reaction time
$$\begin{matrix} & \ \rightarrow \text{~}\text{Descending order of reaction time}\text{~} \\ & \ \Rightarrow t_{B} > t_{E} > t_{A} > t_{D} > t_{C} \\ & \ \rightarrow \text{~}\text{Descending order of distance covered}\text{~} \\ & \ \Rightarrow S_{B} > S_{E} > S_{A} > S_{D} > S_{C} \end{matrix}$$
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