Answer:
a) always. b) electric field lines are defined by the path positive test charges travel.
Explanation:
By convention, field lines always follow the direction that it would take a positive test charge (small enough so it can´t disrupt the field created by a charge distribution), under the influence of an electric field, at the same point where the test charge is located.
So any positive charge, subject to an electric field influence, moves along the field line that passes through its current position, in the same way that a positive test charge would.
We could say also that the electric force on a positively charged particle is in the same direction as the electric field that produces that force (due to some charge distribution) , which is true, but it doesn´t explain why.
Hi there!

We know that:

U = Potential Energy (J)
K = Kinetic Energy (J)
E = Total Energy (J)
At 10m, the total amount of energy is equivalent to:
U + K = 50 + 50 = 100 J
To find the highest point the object can travel, K = 0 J and U is at a maximum of 100 J, so:
100J = mgh
We know at 10m U = 50J, so we can solve for mass. Let g = 10 m/s².
50J = 10(10)m
m = 1/2 kg
Now, solve for height given that E = 100 J:
100J = 1/2(10)h
100J = 5h
<u>h = 20 meters</u>
I believe that the correct given values are:
density = 755 kg/m^3
volume = 640 cm^3
First let us convert volume to m^3 units.
volume = 640 cm^3 * (1 m / 100 cm)^3 = 6.4 x 10^-4 m^3
so the mass is:
mass = 755 kg/m^3 * (6.4 x 10^-4 m^3)
<span>mass = 0.4832 kg = 483.2 g</span>
The second answer choice is not true (ozone is concentrated in the stratosphere, not the exosphere)