Sand falls vertically onto a horizontal conveyor belt at a steady rate of $2\ \text{kg/s}$, as shown in the figure. The belt moves at a constant speed of $3\ \text{m/s}$, and the sand is carried along with it. Ignore friction in the rollers. The extra force needed to keep the belt moving at a steady speed, and the extra power the motor must supply, are

Fig. 1: Sand falling vertically from a hopper onto a horizontal conveyor belt that moves at 3 m/s.