(A) 
The energy stored by the system is given by

where
P is the power provided
t is the time elapsed
In this case, we have
P = 60 kW = 60,000 W is the power
t = 7 is the time
Therefore, the energy stored by the system is

(B) 4830 rad/s
The rotational energy of the wheel is given by
(1)
where
is the moment of inertia
is the angular velocity
The moment of inertia of the wheel is

where M is the mass and R the radius of the wheel.
We also know that the energy provided is

So we can rearrange eq.(1) to find the angular velocity:

(C) 
The centripetal acceleration of a point on the edge is given by

where
is the angular velocity
R = 0.12 m is the radius of the wheel
Substituting, we find

Answer:
Explained below:
Explanation:
The major limitation in the use of Photovoltaic cells to generate electricity is its unpredictability about the climate that whether it will be a shining day or a cloudy day and it does not work at night also because of no presence of sunlight as it totally depends on it. It can be used as an alternative but cannot be used as chief source of electricity.
It would be D because there is more gravitational forces acting on it than a small block of wood