An electron with charge −e and mass m moves in a circular orbit of radius r around

Explanation:

The electrostatic attraction between the nucleus and the electron is given by:

(1)

where

k is the Coulomb's constant

Ze is the charge of the nucleus

e is the charge of the electron

r is the distance between the electron and the nucleus

This electrostatic attraction provides the centripetal force that keeps the electron in circular motion, which is given by:

(2)

where

m is the mass of the electron

v is the speed of the electron

Combining the two equations (1) and (2), we find

And solving for v, we find an expression for the speed of the electron:

F = 91.2 kp

the correct answer is C

Explanation:

On a first degree lever, the fulcrum (pivot point) is between the weight to be lifted and the force applied. Knowing what force we must apply, write the endowment equilibrium equation.

We will assume that the counterclockwise direction of rotation is positive

             W d₁ - F d₂ = 0

              F = W d₁/ d₂

where

they indicate the value of the weight to lift W = 456 kp and its distance from the fulcrum d₁ = 36 cm; the distance to the applied force (F) is d₂ = 180 cm

let's calculate

            F = 456 36/180

            F = 91.2 kp

therefore the correct answer is C