Q.

When a particle of mass m moves on the x-axis in a potential of the form V(x)=kx2 it performs simple harmonic motion. The corresponding time period is proportional to mk, as can be seen easily using dimensional analysis. However, the motion of a particle can be periodic even when its potential energy increases on both sides of x=0 in a way different from kx2 and its total energy is such that the particle does not escape to infinity. Consider a particle of mass m moving on the x-axis. Its potential energy is V(x)=αx4(α>0) for |x| near the origin and becomes a constant equal to V0 for |x|X0  (see figure).                [2010]

Q.    The acceleration of this particle for |x|>X0  is

1 proportional to V0  
2 proportional to V0mX0  
3 proportional to V0mX0  
4 zero  

Ans.

(4)

F=-dV(x)dx

  As V(x)=constant for x>X0

  F=0 and hence a=0 for x>X0