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Homework Help: Grade 11 Physics Questions

  1. Nov 22, 2004 #1
    Hello,
    Just couple of of Physics questions. I want to make sure I got them right.

    1.How much force (tension must a rope withstand if it is used to accelerate a 1700 kg car at 0.50m/s^2 on a frictionless surface.
    I got:
    [tex](1700)(0.50)[/tex]

    [tex]F=850\frac{kgm}{s^2}[/tex]

    2.A 0.15kg baseball travelling at 35.0m/s strikes the catcher's mitt which recoils backwards 10 cm as it brings the ball to rest.
    A) What was the force applied by the ball on the glove?
    [tex](0.15)(35)[/tex]
    [tex]F=5.25\frac{kgm}{s^2}[/tex]
    B) What was the force applied by the glove on the ball?
    I don't know how to do this one

    3.A parachutist is moving downward with a force due to gravity of 630N experience a a fricitonal air resistence of 450N.
    A)Calculate the acceleration of the parachutist.
    [tex]630-450=180M(Down)[/tex]
    B)Calclation the acceleration of the block.

    [tex]A=\frac{F}{M}[/tex]

    [tex]F=(M)(G)[/tex]

    [tex]180=(M)(9.8)[/tex]

    [tex]M=\frac{180}{9.8}[/tex]

    [tex]M=18.36[/tex]

    [tex]A=\frac{180}{18.36}[/tex]

    [tex]A=9.8[/tex]
     
  2. jcsd
  3. Nov 22, 2004 #2
    I don't like the last two. For the third you are right up until F = MG where you for some reason assume the mass is variable with force as opposed to the acceleration. For #2, use the fact that [tex]v_f^2 = v_i^2 + 2ad[/tex] to find the acceleration. From there it's trivial to find the force.
     
  4. Nov 22, 2004 #3
    What do you mean you don't like them??

    Anyway Raza, for question 2(b) you need to know Newton's Third Law: the magntiude force [tex]F_{AB}[/tex] on A due to B equals the magnitude of the force on B due to A, [tex]F_{BA}[/tex] and these forces are equal and opposite:

    [tex]\vec{F_{AB}} = -\vec{F_{BA}}[/tex]

    Hope that helps.

    Cheers
    Vivek
     
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