A particle of mass m is released from rest and follows a parabolic path as shown. Assuming that the displacement of the mass from the origin is small, which graph correctly depicts the position of the particle as a function of time? [figure]
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Answer
(2) [figure]
Solution
The potential energy curve is a parabola: V(x) = 12kx2
F = - dVdx = -kx
For small displacements, the particle executes SHM about the origin, so x(t) is a sinusoidal (smooth) curve, not a zig-zag of straight lines.
The particle is released from rest at a positive x, i.e. at the extreme position x = +A.
x(t) = A t: x starts at its maximum positive value and decreases.
Only graph (2) shows this.
Answer: (2)