A paddle wheel is coupled to a mass of 12 kg via fixed frictionless...

The work done on the liquid by the paddle wheel is equal to the decrease in the potential energy of the falling mass. Since the block falls slowly, there is no change in its kinetic energy.

The work done is given by:

$W = mgh$

Given:
Mass of the block, $m = 12 \text{ kg}$
Distance fallen, $h = 70 \text{ cm} = 0.7 \text{ m}$
Acceleration due to gravity, $g = 10 \text{ m/s}^2$

Substituting the values:

$W = 12 \times 10 \times 0.7$

$W = 84 \text{ J}$