Final answer:
Without bedrock, the ultimate bearing capacity of the soil under a foundation is likely lower. For gravitational potential energy, a brick at 4m height has 39.24 joules of energy, which becomes 0 once it falls to the ground.
Step-by-step explanation:
The ultimate bearing capacity of a foundation refers to the maximum load per unit area that the soil or rock beneath a foundation can withstand without leading to shear failure. In the case where there is no bedrock for at least 4m below the foundation, the ultimate bearing capacity would be determined by the shear strength characteristics and the compressibility of the soil that is present instead of the bedrock.
It is common for soils to have a lower bearing capacity compared to bedrock, so without bedrock, the calculated ultimate bearing capacity is likely to be lower.
Regarding the question of the gravitational potential energy (GPE), we use the formula GPE = mgh, where m is the mass in kilograms, g is the acceleration due to gravity (9.81 m/s² on Earth), and h is the height above the reference point in meters.
At the top of a 4m high roof, the brick would have a GPE of 1 kg × 9.81 m/s² × 4 m = 39.24 joules.
Once the brick has fallen to the ground, its GPE would be 0, as it is no longer elevated above the reference point.