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!

Dropping from 4 times the height, how much longer does it take?

  1. Dec 17, 2011 #1
    We solved this in class 4 months ago but I just can't remember the solution, or even where to start. I remember rearranging an equation. If an object is dropped from a height and it takes T seconds to hit the ground, how long will it take if dropped from four times the height?

    Possible answers:

    A. T seconds.
    B. √2 T seconds.
    C. 2T seconds.
    D. 2 √2 T seconds.
    E. 4T seconds.

    Can anyone give me a hint without giving the answer?
     
  2. jcsd
  3. Dec 17, 2011 #2

    Delphi51

    User Avatar
    Homework Helper

    We aren't supposed to help until we see an attempt but just this once I can't resist.
    The approach to any problem is to first realize what is going on and write equations that apply to it. In this case, accelerated motion is going on. Can you write equations that apply?
     
  4. Dec 17, 2011 #3
    Is it by rearranging s= ut + .5at2?
     
  5. Dec 17, 2011 #4

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Yes, and of course, the initial velocity u is zero.
     
  6. Dec 17, 2011 #5
    I keep getting the answer as 2T, is that right? When we did it months ago I'm almost positive it had a root2 in the answer
     
  7. Dec 17, 2011 #6

    Dick

    User Avatar
    Science Advisor
    Homework Helper

    Sure that's right. If the displacement changes by a factor 4, T changes by a factor of 2. You might be thinking of a different problem.
     
  8. Dec 17, 2011 #7
    I must be, that's the only thing that was throwing me off since I first saw the question. I thought I remembered a root2 in there so I was doubting the obvious answer of 2T! Anyway, thank you. :)
     
  9. Dec 17, 2011 #8

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Yes, 2T is correct.

    When the problem was done earlier, in class, was it exactly the same, or just similar. After all, 2=√4 .
     
  10. Dec 17, 2011 #9
    That's true, but for some reason √2 was stuck in my head. At least I know now for incase it comes up in the exam in January, because I would have doubted myself and picked one of the √2 answers.
     
  11. Dec 17, 2011 #10

    PeterO

    User Avatar
    Homework Helper

    When you do the exam in January, are you allowed to take in a self-prepared "formula sheet" or page of notes?
     
  12. Dec 18, 2011 #11
    We are given a formula sheet but I'm not sure if we'e allowed to add anything to it. I planned on finding that out when we go back. Luckily it gives the equations I have the hardest time remembering or being able to prove to myself. I wish we were allowed to take in a page of notes for Algebra... not looking forward to that!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook