Recent content by goodboy

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    How to get the constraint equation of this problem

    A particle moves in the xy plane under the constraint that its velocity vector is always directed towards a point on the x-axis whose abscissa is some given function of time f(t). Show that for f(t) differentiable, but otherwise arbitrary, the constraint is nonholonomic...
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    Where does the energy come from?

    put a iron beside a magnet,then we konw the iron would be attracted toward the magnet.but where does the kinetic energy of the iron come from?
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    Moment of inertia and Center of mass

    calculate the MOI. first assume the coodinat of the axis is (x,y,z).and the distance from points to axis are known as ri.then the MOI =Σmiri^2 or ∫ρiri^2dl do you think it is right?
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    Help this problem cost me much time

    thank you very much,my first language is chinese.i'm not good at english,don't laugh at me . there is no problem in your interpretation.
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    Help,this problem cost me much time

    How to get this conclusion if we know the magnetic moment m,and the magnetic induction B.then the force is who can tell me how to get this.thanks very much
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    Final velocity of both vehicles

    momentum is a vector,in your first equation "2"means what? my solution like this: P1sin(14)+P2cos(14)=P P1cos(14)=P2sin(14) P3=√(2mfs) there P1 is the momentum of the truck , P2 is the momentum of the sport car. P is the final momentum of both vehicles m=m1+m2...
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    Help this problem cost me much time

    english is my second language,if there are some wrong in the sentence ,don't laugh at me :redface: dig a columniform cavity in a infinity uniformity magnetic medium.the cavity's radius is r and the high is h,and the axis of the cavity parallels the direction of magnetization M in the...
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    Why is the Electric Field in a Conductor Zero After Removing Negative Charge?

    a problem.put a conductor in a electric field .then we konw that in the conductor ,the positive charge will move along with the direction of the electric field,and the negative charge will move along against the direction of the field.then at all point in the conductor ,the external field+the...
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    How Do You Calculate the Time Interval Between Bounces of a Ball?

    20.2=9.81/2*t^2,=>t=2.03 or 20.2 = 19.90792t - 9.81/2*t^2
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