Answer:
t = 2.58*10^-6 s
Explanation:
For a nonconducting sphere you have that the value of the electric field, depends of the region:

k: Coulomb's constant = 8.98*10^9 Nm^2/C^2
R: radius of the sphere = 10.0/2 = 5.0cm=0.005m
In this case you can assume that the proton is in the region for r > R. Furthermore you use the secon Newton law in order to find the acceleration of the proton produced by the force:

Due to the proton is just outside the surface you can use r=R and calculate the acceleration. Also, you take into account the charge density of the sphere in order to compute the total charge:

with this values of a you can use the following formula:

hence, the time that the proton takes to reach a speed of 2550km is 2.58*10^-6 s
Answer:
The current is 2.0 A.
(A) is correct option.
Explanation:
Given that,
Length = 150 m
Radius = 0.15 mm
Current density
We need to calculate the current
Using formula of current density


Where, J = current density
A = area
I = current
Put the value into the formula


Hence, The current is 2.0 A.