Final answer:
The question is about calculating the gravitational potential energy and kinetic energy of a falling brick.
Step-by-step explanation:
The subject of this question is Physics. Specifically, it deals with the concept of gravitational potential energy and kinetic energy.
To calculate the gravitational potential energy of the brick at the top of the roof, we use the formula PE = mgh, where m is the mass of the brick, g is the acceleration due to gravity, and h is the height.
To calculate the kinetic energy of the brick when it reaches the ground, we use the formula KE = 1/2mv^2, where v is the velocity of the brick.
For the given scenario, we have a brick with a mass of 1 kg and a height of 4 m. Plugging these values into the formulas, we find that the gravitational potential energy at the top of the roof is 39.2 J and the kinetic energy when it reaches the ground is also 39.2 J.
The question concerns a 4.80 kg watermelon being dropped from rest from the top of an 18.0 m building. The concept at play here is related to Physics, specifically to the study of mechanics and the free fall motion of objects under the influence of gravity.
This type of problem requires understanding of gravitational potential energy, kinetic energy, and the equations of motion for an object in free fall.
To determine certain properties of the watermelon's fall such as the time it takes to reach the ground or its impact velocity, we would use the acceleration due to gravity (9.8 m/s²) and kinematic equations.
For instance, the potential energy at the top would be calculated using the formula PE = mgh, where m is the mass of the watermelon, g is the acceleration due to gravity, and h is the height from which it was dropped.