Answer: The electron number density (the number of electrons per unit volume) in the wire is
.
Explanation:
Given: Current = 5.0 A
Area = 
Density = 2.7
, Molar mass = 27 g
The electron density is calculated as follows.

where,
= density
M = molar mass
= Avogadro's number
Substitute the values into above formula as follows.

Thus, we can conclude that the electron number density (the number of electrons per unit volume) in the wire is
.
It could be warmer solid, or liquid, or gas, depending on the pressure and the amount of heat added.
a) The change in momentum of the ball is given by:

where m=140 g=0.14 kg is the mass of the ball, and
is the change in velocity. Substituting, we find

The ball stops in t=1.5 ms=0.0015 s; the magnitude of the force that stops the baseball is given by the ratio between the change in momentum and the time taken:

b) The force we found at point a) is the force that the head exerts on the ball to stop it. However, Newton's third law states that when an object A exerts a force on an object B, object B also exerts a force equal and opposite on object A. If we apply this law to this case, we understand that the force exerted by the baseball on the head is equal to the force exerted by the head on the ball: therefore, the answer is still 2.8 kN.
c) The forehead is not in danger of a fracture, since it can withstand a maximum force of 6.0 kN, while the ball exerts a force of 2.8 kN. Instead, the cheek is in danger of fracture, because it can withstand only a maximum force of 1.3 kN.
An object's momentum will change if there is a non-zero net external force acting on it. This assertion is true.
<h3>
</h3><h3>What is momentum?</h3>
The momentum is defined as the product of mass and the velocity of the body. It is denoted by the letter P. It occurs due to the applied force. Its unit is Kg m/s².
p=mΔV
If there is a change in the velocity there must be a force acting on the object.
If an object is acted on by a non-zero net external force, its momentum will not remain constant. is an accurate statement.
<h3>
</h3>
Hence, option B is correct.
To learn more about the momentum refer to the link;
brainly.com/question/4956182
#SPJ1