The potential energy function for a particle executing linear simple harmonic motion is given by V(x)=k x^{2} / 2, where k is the force constant of the oscillator. For k=0.5 \mathrm{~N} m^{-1}, the graph of \mathrm{V}(\mathbf{x}) versus \mathrm{x} is shown in Figure. Show that a particle of total energy 1 \mathrm{~J} moving under this potential must ‘turn back’ when it reaches x=\pm 2 \mathbf{m}.
The potential energy function for a particle executing linear simple harmonic motion is given by V(x)=k x^{2} / 2, where k is the force constant of the oscillator. For k=0.5 \mathrm{~N} m^{-1}, the graph of \mathrm{V}(\mathbf{x}) versus \mathrm{x} is shown in Figure. Show that a particle of total energy 1 \mathrm{~J} moving under this potential must ‘turn back’ when it reaches x=\pm 2 \mathbf{m}.

Solution:

Energy of the particle will be, \mathrm{E}=1 \mathrm{~J}

\mathrm{K}=0.5 \mathrm{~N} \mathrm{~m}^{-1}

\mathrm{K} . \mathrm{E}=\frac{1}{2} \mathrm{mv}^{2}

Based on law of conservation of energy, we can write,

E=V+K

1=\frac{1}{2} \mathrm{kx}^{2}+\frac{1}{2} \mathrm{mv}^{2}

When it turns back, velocity becomes zero, so

1=\frac{1}{2} \mathrm{kx}^{2}

\frac{1}{2} \times 0.5 x^{2}=1

x^{2}=4

x=\pm 2

Thus, the particle turns back on reaching \mathrm{x}=\pm 2 \mathrm{~m}.