<h2>Hello!</h2>
The answer is: Coulomb's law equation.
<h2>Why?</h2>
The Coulomb's law states that the strength of an electric field (between two charges) can be calculated by multiplying their charges and dividing it into the square of the distance between their centers.

Where:
E = Electric Field Strenght


d = separation between charges (m)
Have a nice day!
Answer:
V1 =8.1 m/s
Explanation:
height at highest point (h2) = 4.1 m
height at lowest point (h1) = 0.8 m
acceleration due to gravity (g) = 9.8 m/s^{2}
from conservation of energy, the total energy at the lowest point will be the same as the total energy at the highest point. therefore
mgh1 +
= mgh2 + 
where
- speed at highest point = V2
- speed at lowest point = V1
- mass of the girl and swing = m
- at the highest point, the speed is minimum (V1 = 0)
- at the lowest point the speed is maximum (V2 is the maximum speed)
- therefore the equation becomes mgh1 +
= mgh2
m(gh1 +
) = m(gh2)
gh1 +
= gh2
V1 = 
now we can substitute all required values into the equation above.
V1 = 
V1 = 
V1 =8.1 m/s
Answer:
28.8 meters
Explanation:
We must first determine at which velocity the ball hits the water. To do so we will:
1) Assume no air resistance.
2) Use the Law of conservation of mechanical energy: E=K+P
Where
E is the mechanical energy (which is constant)
K is the kinetic energy.
P is the potential energy.
With this we have
Where:
m is the balls's mass <- we will see that it cancels out and as such we don't need to know it.
v is the speed when it hits the water.
g is the gravitational constant (we will assume g=9.8
.
h is the height from which the ball fell.
Because when we initially drop the ball, all its energy is potential (and
) and when it hits the water, all its energy is kinetic (
. And all that potential was converted to kinetic energy.
Now, from
we can deduce that 
Therefore v=9.6
Now, to answer how deep is the lake we just need to multiply that speed by the time it took the ball to reach the bottom.
So D=9.6
*3
=28.8
Which is our answer.
Without friction, the amount of work only depends on the final height,
and is not affected by the route used to get there.
If the ramp has no friction, then it has no effect on the total amount
of work done. The work to lift the load straight up is the same.
If the ramp has some friction, then it takes more work to use the ramp
than to lift the load straight up. Then the work to lift the load straight up
would be less than when the ramp is used.