Answer:
The final kinetic energy is 
Explanation:
From the question we are told that
The electric field is 
The charge on the object is 
The mass of the object is 
The distance moved by the object is 
The workdone on the object by the fields is mathematically represented as
![W = [qE + mg]d](https://tex.z-dn.net/?f=W%20%3D%20%20%5BqE%20%2B%20mg%5Dd)
Now this workdone is equivalent to the final kinetic energy so
![K = W = [qE + mg]d](https://tex.z-dn.net/?f=K%20%3D%20W%20%3D%20%20%5BqE%20%2B%20mg%5Dd)
substituting values
![K = W = [4.5*10^{-3 } *100 + 0.68 * 9.8]* 1](https://tex.z-dn.net/?f=K%20%3D%20W%20%3D%20%20%5B4.5%2A10%5E%7B-3%20%20%7D%20%2A100%20%20%2B%200.68%20%2A%209.8%5D%2A%201)
Answer:
B.
It will be greater than 10 J.
Explanation:
The total mechanical energy of an object is the sum of its potential energy (PE) and its kinetic energy (KE):
E = PE + KE
According to the law of conservation of energy, when there are no frictional forces on an object, its mechanical energy is conserved.
The potential energy PE is the energy due to the position of the object: the highest the object above the ground, the highest its PE.
The kinetic energy KE is the energy due to the motion of the object: the highest its speed, the largest its KE.
Here at the beginning, when it is at the top of the roof, the baseball has:
PE = 120 J
KE = 10 J
So the total energy is
E = 120 + 10 = 130 J
As the ball falls down, its potential energy decreases, since its height decreases; as a result, since the total energy must remain constant, its kinetic energy increases (as its speed increases).
Therefore, when the ball reaches the ground, its kinetic energy must be greater than 10 J.
