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
Let the total time of fall be $T$. Distance in the last (the $T^{\text{th}}$) second:
$$s_T = \frac{g}{2}(2T - 1) = 5(2T - 1) = 35 \;\Rightarrow\; T = 4\ \text{s}$$
$$h = \frac{1}{2}gT^2 = \frac{1}{2} \times 10 \times 16 = 80\ \text{m}$$
Solution by Sreeraj P, M.Sc Physics