Solution under volume

Step 1: Buoyant force equals the difference in weights.

$F_b = W_{air} - W_{water}$

$F_b = 50\,N - 40\,N = 10\,\mathrm{N}$

Step 2: Buoyant force equals weight of displaced water.

$F_b = \rho_{water} V g$

Step 3: Substitute known values.

$10\,N = (1000\,kg/m^3) V (10\,m/s^2)$

Step 4: Solve for volume $V$.

$V = \frac{10\,N}{(1000\,kg/m^3)(10\,m/s^2)}$

$V = \frac{10}{10000}\,\mathrm{m^3}$

$V = 0.001\,\mathrm{m^3}$

$\boxed{0.001\,m^3}$