B) Tension , is the correct answer
The speed of the rock at 20 m is 34.3 m/s
Explanation:
We can solve this problem by using the law of conservation of energy: the mechanical energy of the rock, sum of its potential energy + its kinetic energy) must be conserved in absence of air resistance. So we can write:
where
:
is the initial potential energy
is the initial kinetic energy
is the final potential energy
is the final kinetic energy
The equation can also be rewritten as follows:
where:
m = 100 kg is the mass of the rock
is the acceleration of gravity
is the initial height
u = 0 is the initial speed (the rock starts at rest)
is the final height of the rock
v is the final speed when h = 20 m
And solving for v, we find:

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The answer is a because tjhey do move at a molecular movemn
Answer:
U = 80.91 J
Explanation:
In order to calculate the electric potential energy between the three charges you use the following formula:
(1)
k: Coulomb's constant = 8.98*10^9Nm^2/C^2
q1: q2 charge
r1,2: distance between charges 1 and 2.
For the three charges you have:
(2)
You use the fact that q1=q2=q3=q and that the distance between charges are equal. Then, in the equation (2) you have:
q = 1.45μC = 1.45*10^-6C
r = 0.700mm = 0.700*10^-3m

The electric potential energy between the three charges is 80.91 J