Conservation of Momentum

Posted on 2006-04-13
Last Modified: 2012-05-05
A wagon with two boxes of gold having a total mass of 300kg is cut loose from horses when it is at rest by a robber. The wagon is at rest 50m up a 6.0 degree slope. The outlaw plans to have the wagon roll down the slope and across a level plane and fall into a canyon where his amigos are waiting. But in a tree 40m from the canyon edge two heros wait. One has mass 75.0kg the other has mass 60.0kg. They drop vertically into the wagon as it passes beneath them.

       *      *        50m                                                   ****
   h  *            *                                                              | |  <---tree
       *                   *                                                       | |
       *           6 degrees *                                                | |
                                                                                      | ------------- 40m -----------------------|

Hope that helps you understand.

a) if they require five seconds to grab the gold and jump out will they make it before the wagon goes over.?

h = 50 sin 6 = 5.23m
v = sqrt(2gh)
v = 10.1m/s

m_c * v = m_cf * v_f

v_f = m_c * v/ m_cf

v_f = 6.97m/s

6.97m/s * 5s = 34.8m, so it looks like they can make it  

b) when they drop into the wagon is the kinetic energy of the system (wagon plus heros) conserved?

    m_i * v_i^2 = m_f * v_f^2

        they are not equal so no.

c) if kinetic energy is not conserved does it increase, decrease and by how much?

The change in kinetic energy is a decrease of 4800 J i get closer to 10000 J so I am doing something wrong.
Question by:BrianGEFF719
    LVL 84

    Expert Comment

    Did you forget to multiply mv^2 by 1/2?
    LVL 19

    Author Comment

    >>Did you forget to multiply mv^2 by 1/2?

    Does that matter if we are comparing two kinetic energies

    K1 = K2
    1/2m_1v_1^2 = 1/2m_2v_2^2

    I just canceled the 1/2 from both sides.
    LVL 84

    Accepted Solution

    canceling the 1/2 does not affect the result of =
    but it can affect the magnitude of the result of -

    Write Comment

    Please enter a first name

    Please enter a last name

    We will never share this with anyone.

    Featured Post

    What Security Threats Are You Missing?

    Enhance your security with threat intelligence from the web. Get trending threat insights on hackers, exploits, and suspicious IP addresses delivered to your inbox with our free Cyber Daily.

    Introduction On a scale of 1 to 10, how would you rate our Product? Many of us have answered that question time and time again. But only a few of us have had the pleasure of receiving a stack of the filled out surveys and being asked to do somethi…
    This article seeks to propel the full implementation of geothermal power plants in Mexico as a renewable energy source.
    Excel styles will make formatting consistent and let you apply and change formatting faster. In this tutorial, you'll learn how to use Excel's built-in styles, how to modify styles, and how to create your own. You'll also learn how to use your custo…
    In this seventh video of the Xpdf series, we discuss and demonstrate the PDFfonts utility, which lists all the fonts used in a PDF file. It does this via a command line interface, making it suitable for use in programs, scripts, batch files — any pl…

    779 members asked questions and received personalized solutions in the past 7 days.

    Join the community of 500,000 technology professionals and ask your questions.

    Join & Ask a Question

    Need Help in Real-Time?

    Connect with top rated Experts

    11 Experts available now in Live!

    Get 1:1 Help Now