Angle of Contact & Capillarity question from MHT CET 2020 (19 Oct, Shift 2)

Answer: (d)

1. Capillary rise $h = \frac{2T\cos\theta}{r\rho g_{\text{eff}}}$, so $h \propto \frac{1}{g_{\text{eff}}}$.
2. Lift going up with acceleration: $g_{\text{eff}} = g + a$, so $h$ decreases.
3. Accelerating train: $g_{\text{eff}} = \sqrt{g^2 + a^2} > g$, so $h$ decreases.
4. Lift going down with $a < g$: $g_{\text{eff}} = g - a < g$, so $h$ increases.
5. So the answer is (d) a lift going down with acceleration $a < g$.