Two small pith balls, each of mass m = 11.2 g, are suspended from the ceiling of the physics lab by 1.7 m long fine strings and are not moving. If the angle which each string makes with the vertical is è = 30.4°, and the charges on the two balls are equal, what is the magnitude of that charge (in µC)? (Please note that the unit of charge is micro-Coulomb here - some browsers might not display the Greek letter mu correctly and show it as an m.)

  1. 👍 0
  2. 👎 0
  3. 👁 1,898
  1. If the charged ball is suspended be the string which is deflected by the angle α, the forces acting on it are: mg (downwards), tension T (along the string - to the pivot point), and F (electric force –along the line connecting the charges).
    Projections on the horizontal and vertical axes are:
    x: T•sin α = F, ….(1)
    y: T•cosα = mg. ….(2)
    Divide (1) by (2):
    T•sin α/ T•cosα = F/mg,
    tan α = F/mg.

    k=9•10^9 N•m²/C²
    F =k•q1•q2/r² = k•q²/(2•L•sinα)².

    tan α = F/mg =
    = k•q²/(2•L•sinα)² •mg.
    q = (2•L•sinα) • sqrt(m•g•tanα/k)=
    =(2•1.7•0.506) •sqrt(0.0112•9.8•0.577/9•10^9) =
    =4.5•10^-6 C =4.5 μC.

    1. 👍 2
    2. 👎 1

Respond to this Question

First Name

Your Response

Similar Questions

  1. Physics

    A loudspeaker of mass 25.0 kg is suspended a distance of 1.00 m below the ceiling by two cables that make equal angles with the ceiling. Each cable has a length of 2.50 m . What is the tension in each of the cables?

  2. Physics

    A loudspeaker of mass 16.0 kg is suspended a distance of h = 2.00 m below the ceiling by two cables that make equal angles with the ceiling. Each cable has a length of l = 2.90 m What is the tension T in each of the cables? Use

  3. physics

    Two identical steel balls, each of mass 5.0 kg, are suspended from strings of length 29 cm so that they touch when in their equilibrium position. We pull one of the balls back until its string makes an angle θ = 25° with the

  4. Physics

    A spring hanging from the ceiling has an unstretched length of 80 cm. A mass is then suspended at rest from the spring causing its length to increase to 89 cm. The mass is pulled down an additional 8 cm and released. What is the

  1. Energy of motion unit test

    A student wants to determine the effect of mass on kinetic energy. She will drop two balls of the same size into a pool of water. Which investigation method should the student use?(1 point) She should drop two balls of the same

  2. Physics

    Two small spheres of mass 451 g and 695 g are suspended from the ceiling at the same point by massless strings of equal length 10.9 m . The lighter sphere is pulled aside through an angle of 65 degrees from the vertical and let

  3. physics

    a small pith ball carries a charge of -1.3 uc. how many excess electrons does this represent?

  4. Science

    A lamp is suspended by a massless string from the ceiling of a descending elevator which decelerates at 1.6 m/s2. If the tension in the string is 82.0 N, what is the mass of the lamp?


    2. Two electronics technicians are looking at the technical manual for a piece of electronic equipment. The manual refers to a particular resistor as a “2.2 megohm resistor.” Technician A says that this means that the


    a 10cm long spring is attached to the ceiling. when a 2.6kg mass is hung from it, the spring stretched to a length of 15cm. what is the spring constant k how long is the spring when a 4.0 kg mass is suspended from it

  3. physics

    Two small plastic balls hang from threads of negligible mass. Each ball has a mass of 0.14g and a charge of magnitude q. the balls are attracted to each other. When in equilibrium, the balls are separated by a distance of 2.05cm

  4. Physics

    Researchers have found that a gecko's foot is covered with hundreds of thousands of small hairs (setae) that allow it to walk up walls and even across ceilings. A single foot pad, which has an area of , can attach to a wall or

You can view more similar questions or ask a new question.