Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Help Exam Tmr! Gr 11 Physics

  1. Nov 6, 2005 #1
    Help Exam Tmr! 112 Physics *FORCES*

    As you may have guessed from the title, I'm in a bit of a bind here. You see the website with the answers to the review questions I'm working on isn't working... and there's an exam tomorrow. Here's a few of the questions any help would be greatly appreciated.
    A 2.0kg fish is hooked on a line that rated to a max of 38 N. At one point, the fish pulls with 40 N of force (fish are weightless in water). What is the min acceration at which you must play out the line to avoid it from snapping?
    A 0.00021 kg spider is suspended from a thin strand of webbing. The greatest tension the strand can withstand without breaking is 0.002 N . What is the max acceleration with which the spider can safetly climb up the strand?

    ok so apparently i need to show my work so here goes:

    for the fish question:
    m= 2.0kg
    Fxrt= 40N
    a = ?

    Fnet canot be more than 38N soo..

    that doesnt seem right to me... awfully fast to make up for 2 N wouldnt you think?
    orr wait..

    Fnet needs to be -2? so then..

    a= -1m/s2


    See the problem with the spider question is this: the Fg of the spider ends up being the same as the max Force... but where Fg is also the net force i should be able to use F=ma... plug that in and you end up with 9.52m/s2... which seems to completely contradict that fact.?.?.?.
    I mean wouldnt the spider only be able to hang there with no acceration at all, unless that is he goes down instead of up... so maybe the answer is -9.52?
    Last edited: Nov 6, 2005
  2. jcsd
  3. Nov 6, 2005 #2
    :zzz: is anyone out there?
  4. Nov 6, 2005 #3


    User Avatar
    Homework Helper

    Force by the FISHING LINE (Tension) needs to be less than 38 N .
    Force by the water (acting on the fish) is known.
    Total Force acting on the fish (as your intuition had it) is 2N.
    total F on fish = (m_fish)(a_fish)

    The total Force acting on the spider looks very small,
    maybe zero depending on the exact "g" value there.
    so, T - mg = 0 = ma = 0
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook