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: Movement of bacterium in the microscope

  1. Jan 17, 2014 #1
    1. The problem statement, all variables and given/known data

    A biologist looking through a microscope sees a bacterium at r1→ = 2.2i + 3.7j -1.2kμm.
    After 6.2s, it's at r2→ = 4.6i + 1.9kμm.
    a)What is it's average velocity
    b) What is its average speed

    3. The attempt at a solution

    v→= Δr/Δt
    v = (r2-r1)/6.2 = (2.4i - 3.7j + 3.1k)μm/6.2s
    = (0.387i -0.596j + 0.5k) μm^-1

    |v| = Δs/Δt
    |v| = SQRT[(2.4)^2i + (-3.7)^2j + (3.1)^2k]/6.2s
    = 0.869μms^-1
  2. jcsd
  3. Jan 17, 2014 #2
    Looks good.
  4. Jan 17, 2014 #3


    User Avatar
    Homework Helper

    Caution: IF it went from the first location to the second location by a long and winding path,
    then the average velocity will be the same but the average speed might have been many times that fast:
    so that is a _minimum_ value for the average speed.
  5. Jan 17, 2014 #4
    If the path was curved, I would have to utilize optimization, am I right?
  6. Jan 19, 2014 #5


    User Avatar
    Homework Helper

    if the path had been curved, you would need to find out long that path was
    by adding each small segment length, found via pythagoras (or integrating the path if given a function with time)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted