The answer is B. The nuclei of elements.
Answer:
Part(a): The final angular velocity is 
Part(b): The ratio of the rotational energies is 
,showing the the energy of th system will decrease.
Explanation:
Part(a):
If '
' be the moment of inertia of an object and '
' be its angular velocity then the angular momentum '
' of the object can be written as
If '
' and '
' be the moment of inertia of the two cylinders and '
' and '
' be the initial angular velocity of the cylinders and '
' and '
' be their respective final angular velocity, then from conservation of angular momentum,
Given, 
. From the above expression
Part(b):
Initial kinetic energy
and Final kinetic energy
Substituting the value of 
,
The above expression shows that the ebergy of the system will decrease.
Hydro electric power is the process of production of electricity from the mechanical energy of water.
In the process of generation of hydro electricity ,large dams are constructed in which the water is stored.The water present at top of the dam has potential energy.The water is driven downward with high pressure. During the falling of water,the potential energy of the water is converted into equivalent kinetic energy. The water coming down with a heavy speed is allowed to fall on a turbine which is connected to a generator.
The mechanical energy of water drives the turbine and electricity is generated due to the electromagnetic induction .
Hence the option A is right i.e falling water that turns the turbine.
Answer:
Inclined plane.
Explanation:
Geometrically, a screw is a narrow inclined plane that is wrapped around a cylinder. Like the other simple machines a screw can amplify force; a small rotational force (torque) on the shaft can exert a large axial force on a load.
A screw is a cylinder with a head (solid top) at one end and a pointed tip (like a nail) at the other end.
The mechanical advantage of the screw depends on the space between the threads and the length (and thickness) of the screw. The closer the threads are, the greater the mechanical advantage. It is easier to drive a screw into an object if the thread spacing is smaller.
<span>Changes in the forms of energy are called "Energy Conversions"
Hope this helps!</span>
