The relations between acceleration and displacement of four particles are given below. Which one of the particles is executing simple harmonic motion?

1. \(a_1 = +2x\) 2. \(a_1= +2x^2\)
3. \(a_1= -2x^2\) 4. \(a_1 = -2x\)
Hint: Use the relation between the acceleration and displacement in SHM.

Explanation: In simple harmonic motion (SHM), the acceleration \(a\) is proportional to the negative displacement from the mean position. The general equation for SHM is: \(a = -\omega^2 x\)
The acceleration should be linear with the displacement and negative sign, indicating that the acceleration is directed toward the mean position (restoring force).
let's analyse each option.
Option 1: \(a_1​=+2x\)
The acceleration is proportional to the displacement, but the sign is positive. This means the force is not directed toward the mean position, so this is not SHM.

Option 2: \(a_2 = +2x^2\)
The acceleration is proportional to \(x^2,\) not to \(x.\) This is non-linear and does not correspond to SHM.
Option 3: \(a_3 = -2x^2\)
Though the sign is negative, the acceleration is proportional to \(x^2,\) which is non-linear. This is not SHM.
Option 4: \(a_4 = -2x\)
The acceleration is proportional to \(x\) with a negative sign, which matches the form of SHM: \(a = -\omega^2 x.\) This particle is undergoing SHM.
Hence, option (4) is the correct answer.