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 .
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.