Un tubo cilindrico hueco de cobre mide 3 m de longitud tienen un diametro exterior de 4cm y un diametro interior de 2 cm¿cuanto pesa?

 W = 9.93 10² N

Explanation:

To solve this exercise we must use the concept of density

           ρ = m / V

the tabulated density of copper is rho = 8966 kg / m³

let's find the volume of the cylindrical tube

           V = A L

           V = π (R_ext  ² - R_int ²) L

let's calculate

          V = π (4² - 2²) 10⁻⁴  3

          V = 1.13 10⁻²  m³

         m = ρ V

        m = 8966 1.13 10⁻²

        m = 1.01 10² kg

the weight of the tube

        W = mg

         W = 1.01 10² 9.8

         W = 9.93 10² N

electric field is a function of 1/r^2

yes, the force per unit charge for a point charge is inverse square law.