Question

When mass is kept constant then terminal velocity for wood is greater or thr iron bob? Nd why

Answer 1

$$v_t\sim d(\rho_s-\rho)$$

d is the diameter of the spherical object, ρ_s is the density of the object, ρ is the density of the fluid.

$$d\sim (\frac{m}{\rho_s})^{\frac{1}{3}}$$

Thus,

$$v_t\sim \rho_s^{-\frac{2}{3}}$$

Then terminal velocity for wood is greater than for iron bob.