JEE Challenger
More from Oscillations

Ratio of Total Mechanical Energies from Phase Space Diagram of SHM

Comprehension Passage

Paragraph for Question Nos. 35 to 37

Phase space diagrams are useful tools in analyzing all kinds of dynamical problems. They are especially useful in studying the changes in motion as initial position and momentum are changed. Here we consider some simple dynamical systems in one-dimension. For such systems, phase space is a plane in which position is plotted along horizontal axis and momentum is plotted along vertical axis. The phase space diagram is x(t)x(t) vs. p(t)p(t) curve in this plane. The arrow on the curve indicates the time flow. For example, the phase space diagram for a particle moving with constant velocity is a straight line as shown in the figure. We use the sign convention in which position or momentum upwards (or to right) is positive and downwards (or to left) is negative.

Passage Diagram 0

The phase space diagram for simple harmonic motion is a circle centered at the origin. In the figure, the two circles represent the same oscillator but for different initial conditions, and E1E_1 and E2E_2 are the total mechanical energies respectively. Then

Diagram 0

Options

A

E1=2E2E_1 = \sqrt{2} E_2

B

E1=2E2E_1 = 2 E_2

C

E1=4E2E_1 = 4 E_2

Correct
D

E1=16E2E_1 = 16 E_2

Topics & Concepts

Step-by-Step Solution

For a simple harmonic oscillator, the total mechanical energy EE is related to the amplitude of oscillation AA by the relation:
E=12kA2E = \frac{1}{2} k A^2
where kk is the force constant of the oscillator.

From the phase space diagram (Momentum vs. Position):

  • The maximum displacement (amplitude) for the inner trajectory corresponding to energy E2E_2 is A2=aA_2 = a.
  • The maximum displacement (amplitude) for the outer trajectory corresponding to energy E1E_1 is A1=2aA_1 = 2a.

Since both trajectories represent the same oscillator, the spring constant kk is identical in both cases.

Thus, the total mechanical energies are given by:
E2=12ka2E_2 = \frac{1}{2} k a^2
E1=12k(2a)2=4(12ka2)=4E2E_1 = \frac{1}{2} k (2a)^2 = 4 \left(\frac{1}{2} k a^2\right) = 4 E_2

Therefore, E1=4E2E_1 = 4 E_2.

Correct Option: (C)