b
The acceleration of bucket is
$a=\frac{2 m g-m g}{3 m}=\frac{g}{3}$ downward
$\therefore P=P_{0}+\rho(g-a) h$
$\therefore P-P_{0}=1000\left(10-\frac{10}{3}\right) \times 0.15$
$\mathrm{P}-\mathrm{P}_{0}=1000 \times \frac{20}{3} \times 0.15$
$\mathrm{P}-\mathrm{P}_{0}=10^{3} \mathrm{N} / \mathrm{m}^{2}=1 \mathrm{kPa}$