The velocity of the rock after 2s is 12.56 m/s.
The velocity of the rock at 25 m upwards is 14.68 m/s.
The velocity of the rock at 25 m downwards is -15.97 m/s.
The given parameters;
- <em>velocity of the rock, u = 20 m/s</em>
- <em>height of the rock, h = 20t - 1.8t²</em>
<em />
The velocity of the rock after 2s is calculated as follows;

The velocity of the rock when the height is 25 m:
h = 20t - 1.8t²
25 = 20t - 1.8t²
1.8t² - 20t + 25 = 0
solve for the time of motion "t" using quadratic formula
a = 1.8, b = -20, c = 25

The value of t that will give 25 m upwards using the motion model is 1.43 s;
h = 20(1.43) - 1.86(1.43)² = 25 m
The velocity of the rock at 25 m upwards (t = 1.43 s) is calculated as follows;

The velocity of the rock at 25 m downwards (t = 9.67 s) is calculated as;

Learn more here:brainly.com/question/25233377