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Thread: Homework Questions

  1. #1
    Senior Engineer
    Join Date
    Dec 2012

    Homework Questions

    Good afternoon everyone,

    Here is my homework question:

    A hot air balloon is ascending at the rate of 12m/s and is 80m above the ground when a package is dropped over the side. (a) How long does the package take to reach the ground? (b) With what speed does it hit the ground?

    Do I set package=-9.8m/s^2 ? A long the y-axis I am going to make up + and down -. V initial balloon=12m/s and we have a height h=80m.

    #2 Question

    Figure 2-26 which is the excel file, depicts a motion of a particle moving along an x-axis with a constant acceleration. The figure's vertical scaling is set by Xs=6.0m. What are the (a) magnitude and (b) the directions of acceleration?

    hm #37.xlsx

    I am not 100% sure how to start this problem... I am assuming I need an equation, but I am not exactly sure how to obtain the equation. Can I use one of the kinematic equations to obtain a formula?

    Thank you everyone for your help.

  2. #2
    Principle Engineer
    Join Date
    Mar 2011
    Judging from the fundamental questions you are asking, you need a fundamental understanding
    of Newton's equations .
    You should either crack a book or get a tutor to give you that help immediately, if not sooner.

  3. #3
    Associate Engineer
    Join Date
    Apr 2013
    How to get started...

    The balloon AND book are BOTH ascending at 12 m/s until the moment of release, which is 80 meters above the ground. The book will continue upward at a slowing rate: the balloon continues at 12 m/s, while the book decelerates at -9.8 m/s*s.
    The book will reach zero velocity at some height GREATER than 80 meters, then accelerate back towards the ground at -9.8 m/s*s.

    So, draw yourself a diagram: initial conditions are velocity 12 m/s, accelleration is -9.8 m/s*s. You want to solve for time (t) when the negative acceleration (towards the Earth, caused by gravity) is going to cancel the postive (up) velocity. At this point velocity = 0.
    Your equation will like Velocity (value = 0 ) = initial velocity (+ 12 m/s) + acceleration over time (-9.8 meters / seconds squared). It's a fairly simple equation to solve for "seconds squared", then take the square root to find seconds.
    This is the time (s) that the book took to come to a stop (in mid air, just for a moment).

    Now you can plug that TIME into an equation for height. The height at which it stopped (V = 0) is the initial height (80 m) plus the distance travelled during the time it took to come to a stop. (I'll let you do your homework on that one and find the right equations.)

    Good luck

    { edit } Being way too generous with homework questions. Please read our TOS. It is kinda-OK to help in vague terms, but I think that last par gave away the farm.
    { /edit }
    Last edited by PinkertonD; 04-08-2013 at 04:20 PM. Reason: Grumpy old Moderator

  4. #4
    Senior Engineer
    Join Date
    Dec 2012
    I had asked a tutor to point me in the right directions for the 2nd question. I used ax^2+bx+c=0 and then for the 1st question I figured out. I feel stupid for not figuring it out sooner. (Haha)

  5. #5
    Senior Engineer
    Join Date
    Dec 2012
    I understand it can be difficult to help me with HW questions without giving me the answer. Thank you.

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