Answer:
According to our principle, when an object is slowing down, the acceleration is in the opposite direction as the velocity. Thus, this object has a negative acceleration. In Example D, the object is moving in the negative direction (i.e., has a negative velocity) and is speeding up.
Explanation:
<span>The answer is 6 Joules. The kinetic energy (KE) of an object is the product of half of the mass (m) of the object and the square of its velocity (v²): KE = 1/2m*v². We know that m = 0.75 kg and that v = 4 m/s. Therefore, KE = 1/2 * 0.75 kg * (4 m/s)² = 1/2 * 0.75 kg * 16 m²/s² = 6 kg*m²/s² = 6 J.</span>
Answer: 15.87 m
From the equation of motion:

where,
is the distance traveled,
is the initial velocity,
is the acceleration and
is the time.
The rock free falls under gravity. Initial velocity,
, 
It took
for rock to hit the water.
Substitute the values in the given equation:

Hence, the water is 15.87 m below the top level of the well.
A reasonable hypothesis would be that, nothing changes with can A (no expansion at all), and Can C is expanding, but Can B is expanding even faster than Can C. (I don't know, if this hypothesis is correct though)