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: Relative Velocity

  1. Jul 24, 2007 #1
    A 3-kg mass is hanging from a 2-kg mass that is hanging from the ceiling of an elevator. The elevator is accelerating upwards at a rate of 2 m/s^2.

    a) Determine the tension in the string connected between the two masses and also in the string between the ceiling and the upper mass.

    b) Repeat for the case where the elevator is accelerating downwards at the same rate.

    c) Is it always the case that the string connected to the ceiling will have a greater amount of tension than the one in between the masses? Justify your answer.

    thank you.

    This is what I got for a:

    sum F on the 2 kg mass:

    4 = T.2 - T.1 - 20
    24 = T.2 - T.1

    sum F on the 3 kg mass:

    6 = T.1 - 20
    T.1 = 26 N
    T.2 = 50 N

    Is this correct?
    Last edited: Jul 24, 2007
  2. jcsd
  3. Jul 24, 2007 #2


    User Avatar
    Science Advisor
    Homework Helper

    You should post this in the homework forum, and you have to at least have a try at a solution before we help you.
  4. Jul 24, 2007 #3


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    You calcualted T.1 incorrectly, and therfore got T.2 wrong also. It should be 6 =T.1 - ?????. Solve for T.1, and then T.2 will come out correct using your first set of equations. What about part b? And for part c, what happens if the elevator is in free fall??l
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook