Answer :
The approximate kinetic energy of the brick just before it touches the ground is 75J. Option A.
Solution:
Mass of brick = m = 2.5 kg
Height of roof = 3 m
Let v be the final velocity of the brick just before hitting the ground.
The kinetic energy of an object is given by KE = [tex]\frac{1}{2} *M *V^{2}[/tex]
v must be calculated before calculating KE.
You can calculate the required variables using the formula where u is the initial velocity, v is the final velocity, a is the acceleration, and s is the distance traveled.
Where s = roof height, u = 0 because the brick falls instead of being thrown, so a = gravitational acceleration = g = 9.8.[tex]\frac{M}{S^{2} }[/tex]
So[tex]V^{2}[/tex] = 0+2x9.8x3 = 58.8
So v = [tex]\sqrt{58.8}[/tex] = 7.66m/s
Now we can calculate the kinetic energy = [tex]\frac{1}{2} *m*v^{2} = \frac{1}{2} *2.5*58.8 = 73.5 kg*\frac{m^{2} }{s^{2} }[/tex]
We also need to convert KE to Joules.
[tex]1kg*\frac{m^{2} }{s^{2} }[/tex] = 1 joule
Therefore kinetic energy = 73.5 joules.
When an object falls from rest its gravitational potential energy is converted into kinetic energy. Energy conservation as a tool allows us to calculate the velocity just before hitting the surface. When an object hits solid ground, all of its kinetic energy is converted into heat and sound energy. When an object falls to the ground in free fall its potential energy decreases, and its kinetic energy increases.
Learn more about Kinetic energy here:-https://brainly.com/question/25959744
#SPJ4
