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About C30N9

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  1. 1- A toy racing moves with constant speed around the circle shown below. When it is at point A its coordinates are x = 0, y = 3m and its velocity is 6 m/s i. When it is at point B its velocity and acceleration are (respectively)?

    The answer is 6 m/s j and 12 m/s^2 i, respectively. I got the magnitudes right, and I understand why its velocity is in the direction of j. However, why is its acceleration is in the direction i?

    2- Two blocks (A and B) are in contact on a horizontal frictionless surface. A 36-N constant force is applied to A as shown. The magnitude of the force of A on B is?

    3- A 0.20-kg particle moves along the x axis under the influence of a stationary object. The potential energy is given by U(x) = (8.0J/m^2)x^2 + (2.0J/m^4)x^4, where x is in coordinate of the particle. If the particle has a speed of 5.0 m/s when it is at x = 1.0 m, its speed when it is at the origin is?

    (Any relations between potential energy and speed?)

    1. Show previous comments  6 more
    2. C30N9


      @Doom Marine: Wrong. The answer is 11 m/s.

      I'm gonna go and check my physics book and try to figure something out.

    3. Doom Marine

      Doom Marine

      Perhaps the relationship between potential energy and speed in this case is zero-sum. Another idea:

      m*U(x) + 0.5*m*S^2 + m*C = 0.

      I'll pursue that line after I'm done with work.

    4. C30N9


      No need. Found the solution.

      U(1) = 10 J. Kinetic Energy (x) = 0.5 * m * v ^ 2, so KE(1) = 2.5 J because v = 5 m/s when x = 1.

      Mech Energy = U + KE = 12.5 J

      When x = 0 then U = 0 and KE = 0.5 * m * v ^ 2.

      Mech Energy is conserved, so:

      E = 12.5 J --> 12.5 = U + KE --> 12.5 = 0 + 0.5 * m * v ^ 2, so v = 11.48 m/s.

      Thanks anyway.