An object has a charge of -3.5 ? c. how many electrons must be removed so that the charge becomes 1.4 ? c?

When an object loses an electron, it gains more charge and becomes more positively charged. So, if an object originally has a charge of -3.5 x 10⁻⁶ C, it must gain a charge of [ 1.4 x 10⁻6 - (-3.5 x 10⁻⁶) } = 4.9 x 10⁻⁶ C. This results to a final charge of 1.4 x 10⁻6 C. 
Recall that one electron has a charge of 1.6 x 10⁻¹⁹ C. This means that for an object to gain a charge of 4.9 x 10⁻⁶ C, the number of electrons that an object must lose is




Thus, the object must remove a total of 3.06 x 10¹³ electrons.  

Answers: 3.06 x 10¹³ electrons

Assume that . The net force on this object will be (downwards.) The acceleration of this object will be approximately (also downwards.)

Explanation:

Net force

The object is falling towards the ground because of gravity. The size of the gravitational force on this object depends on its mass and the strength of the gravitational field at its location.

Near the surface of the earth, the gravitational field strength is approximately . In other words, approximately of gravitational force acts on each kilogram of mass near the surface of the earth.

The mass of this object is given as . Therefore, the size of the gravitational force on it will be:

.

Near the surface of the earth, gravitational forces point towards the ground. On the other hand, the direction of air resistance on this object will be opposite to its direction of motion. Since this objects is moving towards the ground, the air resistance on it will be directed in the opposite direction. That's exactly the opposite of the direction of the gravitational force on this object. The net force on this object will be:

.

Acceleration

Let denote the acceleration on this object. Apply Newton's Second Law of motion:

.

Note that the acceleration of this object and the net force on it should be in the same direction.