Recent content by MasterNewbie

  1. M

    Time derivative of relativistic momentum help

    It is left there because c (and c^2) is a constant.
  2. M

    Find gravitational potential inside uniform ball

    The potential would be constant in that case. This isn't consistent with the problem, though, since the potential I am supposed to be getting is mg/2R*(r^2-3R^2) which isn't constant. I just erased some previous work since I thought I discovered an error but it doesn't change anything as far...
  3. M

    Find gravitational potential inside uniform ball

    Homework Statement Find the potential and force on a mass m outside and inside the Earth in terms of g, the acceleration due to gravity, assuming Earth has uniform density and radius R.Homework Equations For a mass m, the potential energy of it in the gravitational field of a spherical shell of...
  4. M

    Time derivative of relativistic momentum help

    Chain rule. Since v is a function of t, the time derivative of 1-v^2/c^2 is -2v(dv/dt)/c^2. https://www.physicsforums.com/showthread.php?t=343032 I posted a similar question a year after this one if you want a second angle.
  5. M

    Moment of inertia of a hoop about a point

    I dug through my mechanics book, and there is an equation you can use to calculate the components of the inertia tensor about any point, if you know the components of the tensor about the center or mass. Keeping in mind the point is displaced from the cm by (x,y,z) (so for mine x=z=0, y=-r)...
  6. M

    Moment of inertia of a hoop about a point

    Homework Statement Find the moment of inertia of a circular wire hoop about a point on the hoop. mass = m radius = r Homework Equations Izz = Iyy + IxxThe Attempt at a Solution Well, using the above equation I first tried to solve for Ixx. Since we are looking for the moment of inertia about a...
  7. M

    Relativistic version of Newton's second law with parallel force

    Yeah, I did the derivative wrong, I forgot to do chain rule for the v2 so the derivative of γ would be γ3*va/c2 So then dp/dt = γma[γ2(v/c)2+1]. Assuming the math I did was right the only way I could get what I'm looking for is if (v/c)2 is equal to 1-1/γ2 so when you distribute you'd get...
  8. M

    Relativistic version of Newton's second law with parallel force

    Homework Statement "Given F=dp/dt. If the force is parallel to velocity show that F=γ3ma." Homework Equations F=dp/dt and p=γmv The Attempt at a Solution Since the force is the first derivative of the momentum with respect to time, and γ and v both vary with time since there is a...
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