Q 11-02-028NEETJEE MainTop questionMedium
A stone dropped from rest covers $35$ m in the last second of its fall. From what height was it dropped? ($g = 10\ \text{m/s}^2$)
Answer: (A) $80$ m
Concept. From rest, the distance in the $T$th second is $\dfrac{g}{2}(2T - 1)$; then $h = \dfrac12gT^2$.
Step 1. Total time. $5(2T - 1) = 35 \Rightarrow T = 4$ s.
Step 2. Height. $h = \dfrac12 \times 10 \times 16 = 80$ m.
Answer. $80$ m (Option A).
Solution by Sreeraj P, M.Sc Physics