What is the force and acceleration in a conical pendulum?

[brmochel]

This homework is worth 5 percent of the total grade, so this shows that I am purely doing this for my own benefit. I'm struggling with this course, want to understand it, and will be taking more physics classes in the future college courses that I take. In conclusion to this, I ask that instead of just telling the answer, that you explain why something is what it is and provide physical intuition to back and support your assumptions.

Question 1:
In the Bohr model of the hydrogen atom, the speed of the electron is approx 2.20*10^6 m/s.
Find (a) the force acting on the electron as it revolves in a circular orbit of radius 0.530*10^-10 m and (b) the centripetal acceleration of the electron.

Attempt at Question 1:
I couldn't solve for a, but I recognized centripetal acc. in the second part of the question and know the formula as v^2/r..Centripetal Acc.=2.20*10^6/.530*10^-10..the number was astronomical and thus didn't seem like a logical answer.

Question 2:
Consider a conical pendulum with an 80.0-kg bob on a 10.0-m wire making an angle of 5.00 degrees with the vertical. Determine (a) the horizontal and vertical components of the force exerted by the wire on the pendulum and (b) the radial acceleration of the bob.

Attempt at Question 2:
I was able to draw a picture forming a right triangle, allowing me to solve for the radius that will help with solving for part b of the problem. I wasn't able to get the part a though..Are they asking for me to draw a free-body diagram for the horizontal and vertical forces? Helpp! Skipping part a, I tried solving part b. I solved the radius by taking sin 5=r/10
r=.872 meters. Now, I just didn't understand how to go any further with only 1 known and 2 unknowns..

Question 3:
An object of mass 5 kg attached to a spring scale rests on a frictionless, horizontal surface. The spring scale, attached to the front end of a boxcar has a constant reading of 18N when the car is in motion. (a) if the spring scale reads zero when the car is at rest, determine the acceleration of the car. (b) What constant reading will the spring scale show if the car moves with constant velocity? (c) Describe the forces on the object as observed by someone in the car and by someone at rest outside the car.

Attempt at Question 3:
For part a, I was able to solve by using the formula f=ma. I used 18 N as f and 5 for m..I solved for acceleration=18/5 m/s^2..Was this correct and was it what they were asking for in part a? for part b, I reasoned that since it would be moving with constant velocity, the scale would still be 18 N..is this correct? For part c, I didn't know exactly what to put..helpp

 

[brmochel]

You can help with any of the questions, you don't have to do all of them.

 

[Astronuc]

For a) what forces are in balance for a revolving electron?

For b) gravity is always acting downward on a mass. What are the other forces?

For c) remember F = ma and F = kx. What is the significance of F, a? What is the significance of constant velocity?

 

[brmochel]

Can you specify which question you are answering. I understand the first one to go with the first question. Not sure which ones you were helping with for the b and c. What is kx? is that friction ? Constant velocity means that there isn't an acceleration

 

[brmochel]

In response to the part b , you would also have an upward force equal to the downward gravity, correct? Isn't that the net force?

 

[brmochel]

or normal ?

 

[Quinzio]

Question 1:
part b seems ok, you've got big numbers but you're dealing with microscopic object so it's no wonder.
part a what there is in the middle of an atom ? can it interact with an electron ?

 

[Quinzio]

Can you specify which question you are answering. I understand the first one to go with the first question. Not sure which ones you were helping with for the b and c. What is kx? is that friction ?

Nope, look how springs work Hooke's law http://en.wikipedia.org/wiki/Hooke's_law

You seem able to do it on yourself.

 

[brmochel]

Question 1: part a: are they asking for a specific force, such as 5 Newtons? There is a nucleus which consists of protons and neutrons; the electrons are revolving around this.

Perhaps they are also wanting the centripetal force, which would involve me to use this formula:
fc=mac (centripetal force=mass * centripetal acceleration)

This doesn't make sense either because why would they give a part a which requires an answer from part b to solve for a lol?