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Questions in Newtons Laws and Thermodynamimcs.

  1. Jan 19, 2013 #1
    Hi there can anyone please explain to me these questions I am really confused about them.

    Q: A 15 kg wagon is pulled to the right a force of 45 newtons. the wagon accelarates at 2 m/s2. what is the net (unbalanced) force accelerating the wagon? (f of g is 10)

    the book says the answer is 30, but i have no idea why?

    Q: If 200 grams of water at 48 C is mixed with 100 grams of water at 30 c, the resulting temp. of the water is?

    I wanted to use the mc(delta)t equation but they dont give the specific heat of water in the question.

    Q: If all of the forces acting on an object balance so that the net force is zero, then:
    A) the object must be at rest (i chose this answer but its wrong IDK why)
    B)the object speed will decrease
    E) none of the above( this is the answer according to the book.

    Q: at the surface of the earth, an object of mass m has weight w. If this object is transported to an altitude thats twice the radius of the earth then at the new location the mass and weight is?

    i said the mass is m because its an intrinsic property but i dont know what the wieght would be.

    please help me out, i am studying for a test and i really need to clear these concepts.
  2. jcsd
  3. Jan 19, 2013 #2
    Maybe. m=15 kg and the force F=45N, it accelerates by 2m/s/s then
    [itex] F_{net} = ma = 15\text{kg}\times 2\text{m/s^2} = 30 \text{N}[/itex]
  4. Jan 19, 2013 #3
    The 2nd question. Find it yourself, it must be this equation you are to use, else it is complicated I think.
    3rd question: Newtons 1st law says that a particle which is affected by no force is continuing with the same velocity along a straight line, thus if it had e.g. v = 400m/s as velocity it would still be moving with that velocity not increasing nor decreasing.
    4. I think you should use the gravitational formula [itex] F_{grav} = -G\dfrac{mM_{earth}}{r}[/itex] then compare that force to the usual F = mg
  5. Jan 19, 2013 #4
    ok thanks
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