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: Mass Question

  1. Sep 23, 2007 #1
    1. The problem statement, all variables and given/known data
    A lamp hangs vertically from a cord in a descending elevator that decelerates at 1.4 m/s2. (a) If the tension in the cord is 56 N, what is the lamp's mass? (b) What is the cord's tension when the elevator ascends with an upward acceleration of 1.4 m/s2?


    2. Relevant equations
    T-mg=ma


    3. The attempt at a solution
    I got part (b) to be 56 N and that was correct but then I used the formula... but I don't know how to solve for mass for part (a) when there are two masses in the equation above, I know T to be 56N and g to be 9.8m/s squared also a to be 1.4m/s squared... Can anyone help me out? I'm confused.
     
  2. jcsd
  3. Sep 23, 2007 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Just rearrange your initial equation:
    T-mg=ma

    Thus:
    T = mg + ma = m(g +a)

    You take it from here.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook