The charge density of the sheet is 1.384×10⁻⁷C/m².
Charge density is defined as the charge per unit area.
The sheet is a square of length l=17 cm.
Calculate the area A of the sheet .

The charge Q on the sheet is

The charge density σ is given by,

Substitute 4×10⁻⁹C for Q and 0.0289 m² for A.

Thus, the charge density of the sheet is <u>1.384×10⁻⁷C/m².</u>
The first law of thermodynamics says that the variation of internal energy of a system is given by:

where Q is the heat delivered by the system, while W is the work done on the system.
We must be careful with the signs here. The sign convention generally used is:
Q positive = Q absorbed by the system
Q negative = Q delivered by the system
W positive = W done on the system
W negative = W done by the system
So, in our problem, the heat is negative because it is releaed by the system:
Q=-1275 J
while the work is positive because it is performed by the surrounding on the system:
W=+855 J
So, the variation of internal energy of the system is
The total energy (also called mechanical energy) is the sum of the kinetic energy and potential energy:

For this pendulum, we see that at t=0.60 s the total energy is TE=0.918 J while the potential energy is 0.054 J, so the kinetic energy (the missing value in the table) is
Explanation:
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