# Electrical Forces help. Two questions

• robinhood1331
In summary, the two particles have potential and kinetic energy at the beginning and end of the experiment. The particle with the larger charge has more potential energy, and the smaller particle has more kinetic energy.
robinhood1331
Did a practice test but I would like to understand these two questions a bit more. I know the answers to both but that doesn't mean anything if i don't get it. Any help would be appreciated

A very small 4.8-g particle carrying a charge of +9.9 μC is fired with an initial speed of directly toward a second small 7.8-g particle carrying a charge of + The second particle is held fixed throughout this process. If these particles are initially very far apart, what is the closest they get to each other? (k = 1/4πε0 = 9.0 × 109 N • m2/C2)

Two tiny beads, each of mass 3.2 g, carry equal-magnitude charges. When they are placed 6.4 cm apart and released in outer space, they begin to accelerate toward each other at 538 m/s2. What is the magnitude of the charge on each bead? (k = 1/4πε0 = 9.0 × 109 N • m2/C2)

Welcome to PF;
Those are great questions - please tell us how you understand them so we can see how best to help you.
i.e. there are a number approaches - how would you go about finding the answers and what is your reasoning along the way?

In Classical Physics
1. Force = mass x acceleration.
2. Energy = ½ x mass x (velocity²) = Force x distance = ...
3. Simple math requires Position(now) = Position(then) + (velocity(then))x(time interval between then and now) + ½ x acceleration x (time interval between then and now²)
4. Velocity(now) = velocity(then) + acceleration(between then and now) x (time interval)
5. Two common forces are electrical and gravitational. Both follow inverse square laws (in simple situations). The inverse square law is F = kPp/(r²) where F=force, k is a constant of Nature, r is distance between particles and P and p are quantities associated with the Law (mass or charge in these two cases) of Particle1 and particle2.
6. momentum = velocity x mass
7a. >>and most important<< energy (including potential energy) is conserved.
7b. >>and just as important<< momentum is conserved.
All the rest is algebra (and geometry).

Simon Bridge said:
Welcome to PF;
Those are great questions - please tell us how you understand them so we can see how best to help you.
i.e. there are a number approaches - how would you go about finding the answers and what is your reasoning along the way?

Its been over a year since I've taken physics 1. My practice was for physics 2 which I'm finally taking. All the other questions I was able to answer but these two seem to borrow concepts from physics 1 so I'm a bit clueless.

I figured for the second question, I'd solve for force=ma and then solve for the charges given coulombs law since I have the force. Thats what I'm doing but I'm not getting 890 nC which is the answer.

F= ( 3.2g)(538 m/s)
F=1721.5

F = kPp/(r²) and solve for P.

Edit: Forgot to change the units for question 2. I guess that's what happens when you take so long to take physics 2. Help would still be appreciated for question 1! I noticed I was missing information when I posted it.

A very small 4.8-g particle carrying a charge of +9.9 μC is fired with an initial speed 8.0 m/s of directly toward a second small 7.8-g particle carrying a charge of +5.2 μC + The second particle is held fixed throughout this process. If these particles are initially very far apart, what is the closest they get to each other? (k = 1/4πε0 = 9.0 × 109 N • m2/C2)

Last edited:
Yah - for Q2 you can just use that the force is equal to the mass times acceleration - and Coulombs force law.
The other approach is to say that the force is proportional to the gradient of the potential energy.

Q1 uses conservation of energy - or the Work-energy theorem.
Start out by describing the initial and final conditions in terms of potential and kinetic energy.

## What are electrical forces?

Electrical forces are forces that exist between charged particles, such as protons and electrons. They can either attract or repel each other depending on their charges. These forces are responsible for many everyday phenomena, such as static electricity and the functioning of electric circuits.

## What is the difference between electric force and electric field?

Electric force refers to the actual force that exists between two charged particles, while electric field refers to the region around a charged particle where the force can be felt. Electric field is a vector quantity, meaning it has both magnitude and direction, while electric force is a scalar quantity, meaning it only has magnitude.

## How do you calculate the strength of an electric force?

The strength of an electric force can be calculated using Coulomb's Law, which states that the force between two charged particles is directly proportional to the product of their charges and inversely proportional to the square of the distance between them. The formula is F = k(q1q2)/r^2, where F is the force, k is a constant, q1 and q2 are the charges of the particles, and r is the distance between them.

## What is an electric dipole?

An electric dipole is a pair of equal and opposite charges that are separated by a small distance. This creates a dipole moment, which is a measure of the strength and direction of the dipole. Electric dipoles are important in understanding the behavior of molecules and atoms.

## How do electrical forces play a role in everyday life?

Electrical forces are essential for modern technology and play a crucial role in our daily lives. They are responsible for the functioning of electronic devices, such as phones and computers, and power our homes and businesses. Electrical forces also play a role in natural phenomena, such as lightning and the movement of charged particles in the Earth's atmosphere.

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