1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Physics 30 electricity problem

  1. Oct 13, 2005 #1
    Ok so im on the last 2 questions of my electricity and electric fields assignment and im totally stumped.
    heres the first one
    12. Object A with a mass of 1.4 X 10-3 kg has a charge of 3.8 X 10-10 C. This object is at rest a distance of 48 cm from a fixed object B of charge 4.2 X 10-5 C. The two objects will repel each other. With what speed will object A be moving at when it is 96 cm from object B?
    (4 marks)
    Ok so far this i figured that first i ahve to find the total energy at rest at 48cm and ET=EP because Ek=0 cuz its at rest. however i cant think of a formula for EP because for EP=mgh i dont have any hieght and for EP=1/2kx^2 i dont have k or x. then i know i find the EP at 96 cm and solve for v, but i cant figure out how to get there.

    THe next question is sort of the same:
    13. Two charged objects A and B have masses of 1.3 X 10-2 kg and 2.6 X 10-2 kg respectively. Their charges are -1.7 X 10-4 C and -3.8 X 10-4 C respectively. They are released from rest when they are 3.6 m apart. What will their speeds be when they are a "large'' distance apart? (6 marks)
    For this one im totally confused because i dont know how to start. I mean i wrote down the variables but im not sure how to approach this question.
    Please help me out... my grade depends on it.
     
  2. jcsd
  3. Oct 15, 2005 #2

    andrevdh

    User Avatar
    Homework Helper

    Try the work done by the electrostatic force as a mass is moved form
    [tex]48\ cm\rightarrow\ 96\ cm[/tex]
    is equal to the change in it's kinetic energy.
     
  4. Oct 15, 2005 #3

    andrevdh

    User Avatar
    Homework Helper

    In the second case all their potential energy gets converted into their kinetic energy.
     
  5. Apr 10, 2011 #4
    try using the potential at the two points then finding out the work done and hence the kinetic energy
    then find the velocity
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook




Loading...
Similar Threads for Physics electricity problem Date
RC Circuit Problem Feb 25, 2018
Meter Bridge. Mar 26, 2016
Hall Voltage Problem Feb 11, 2016
Simple capacitor problem Sep 27, 2015
Electrostatic Problem Sep 24, 2015