Three equal point charges, each with charge 2.00 μC , are placed at the vertices of an equilateral triangle whose sides are of length 0.250 m . What is the electric potential energy U of the system? (Take as zero the potential energy of the three charges when they are infinitely far apart.) U = nothing J

Explanation:

Energy of system of charges

= k q₁q₂ / r₁₂ + k q₁q₃ / r₁₃ + k q₃q₂ / r₃₂

q₁ , q₂ and q₃ are charges and  r₁₂ , r₁₃ , r₃₂ are densities between them

9 x 10⁹ ( 2x2 x10⁻¹²/ .25 + 2x2 x10⁻¹²/ .25 + 2x2 x10⁻¹²/ .25 )

= 9 x 10⁹  x 3 x 16 x 10⁻¹²

= 432 x 10⁻³

= .432 J .

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.