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Gen Physics 1 Help

  1. Mar 5, 2012 #1
    Hey guys, Im new to the forum and could use your help on a few homework problems. Can anyone explain how to do these?
    1. A baseball of mass m and initial speed v strikes a catcher's mitt. If the mitt moves x as it brings the ball to rest, what is the average force it exerts on the ball? expressing in terms of given variables.

    2. A force of magnitude 7.50N pushes three boxes with masses m1=1.30kg, m2=3.20kg, and m3=4.90kg. Find the magnitude of the contact force between boxes 2 and 3.

    3. A farm tractor tows a 3500 kg trailer up a 20 degree incline with a steady speed of 3.0 m/s. What force does the tractor exert on the trailer (ignoring friction)?
  2. jcsd
  3. Mar 5, 2012 #2


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    Staff Emeritus
    Science Advisor
    Gold Member

    Welcome to PF,

    You should familiarize yourself with our rules. We don't do your homework for you here. That would be of no use to you whatsoever.

    However, if you show what you have done so far, we are happy to point out any errors you are making, and even help guide you in the right direction. If you're here to learn physics, and to learn how to use your understanding of physics to solve problems, then you are in the right place!

    All homework help forum posts should be made using the template provided (the thing that you deleted when you typed your post). This is not just to be pedantic on our part. It exists because it is actually a useful way to get you thinking about the problem and how to solve it.

    So, my first question to you would be, what have YOU done on these problems so far?

    For the first problem, what must be done to the ball in order to slow it to rest? Hint: this thing that is "done" to the ball involves two quantities: 1. the force acting on the ball, and 2. the displacement of the ball while the force acts. You know 2, and you are trying to solve for 1.

    For the second problem: draw free body diagrams for each box so that you can take an inventory of the forces that act on each one. Hint: you know the overall acceleration of the entire system because of one of Newton's laws.

    For the third problem, draw a free body diagram for the trailer, indicating all forces that act on it. If the trailer moves at a constant speed, then what must be true about the sum of these forces?
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