To find the mean velocity of the ball while descending the ramp, we can use the formula for mean velocity:
\[ \text{Mean Velocity} = \frac{\text{Total Distance}}{\text{Total Time}} \]
In this case, the total distance is the length of the ramp, which is 77.4 cm, and the total time is 1.8 seconds.
Substituting the values into the formula:
\[ \text{Mean Velocity} = \frac{77.4 \text{ cm}}{1.8 \text{ s}} \approx 43 \text{ cm/s} \]
Therefore, the mean velocity of the ball while descending the ramp is 43 cm/s.