Question:

A particle is in linear simple harmonic motion between two points, A and B, 10 cm apart. Take the direction from A to B as the positive direction and give the signs of velocity, acceleration and force on the particle when it is 

(a) at the end A, 

(b) at the end B, 

(c) at the mid-point of AB going towards A, 

(d) at 2 cm away from B going towards A, 

(e) at 3 cm away from A going towards B, and 

(f) at 4 cm away from B going towards A

Updated On: Nov 2, 2023
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Solution and Explanation

Zero, Positive, Positive 

Zero, Negative, Negative 

Negative, Zero, Zero 

Negative, Negative, Negative 

Zero, Positive, Positive 

Negative, Negative, Negative

Explanation:

The given situation is shown in the following figure. Points A and B are the two end points, with AB = 10 cm. O is the midpoint of the path.

(a, b)

A particle is in linear simple harmonic motion between the end points

At the extreme point A, the particle is at rest momentarily. Hence, its velocity is zero at this point.

Its acceleration is positive as it is directed along AO. Force is also positive in this case as the particle is directed rightward. At the extreme point B, the particle is at rest momentarily. 

Hence, its velocity is zero at this point.

Its acceleration is negative as it is directed along B.

Force is also negative in this case as the particle is directed leftward.

(C)

The particle is executing a simple harmonic motion. O is the mean position of the particle. Its velocity at the mean position O is the maximum. The value for velocity is negative as the particle is directed leftward. The acceleration and force of a particle executing SHM is zero at the mean position.

(d)

The particle is moving toward point O from the end B. This direction of motion is opposite to the conventional positive direction, which is from A to B. Hence, the particle’s velocity and acceleration, and the force on it are all negative.

(e)

The particle is moving toward point O from the end A. This direction of motion is from A to B, which is the conventional positive direction. Hence, the values for velocity, acceleration, and force are all positive.

(f)

This case is similar to the one given in (d).

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Concepts Used:

Simple Harmonic Motion

Simple Harmonic Motion is one of the most simple forms of oscillatory motion that occurs frequently in nature. The quantity of force acting on a particle in SHM is exactly proportional to the displacement of the particle from the equilibrium location. It is given by F = -kx, where k is the force constant and the negative sign indicates that force resists growth in x.

This force is known as the restoring force, and it pulls the particle back to its equilibrium position as opposing displacement increases. N/m is the SI unit of Force.

Types of Simple Harmonic Motion

Linear Simple Harmonic Motion:

When a particle moves to and fro about a fixed point (called equilibrium position) along with a straight line then its motion is called linear Simple Harmonic Motion. For Example spring-mass system

Conditions:

The restoring force or acceleration acting on the particle should always be proportional to the displacement of the particle and directed towards the equilibrium position.

  • – displacement of particle from equilibrium position.
  • – Restoring force
  • - acceleration

Angular Simple Harmonic Motion:

When a system oscillates angular long with respect to a fixed axis then its motion is called angular simple harmonic motion.

Conditions:

The restoring torque (or) Angular acceleration acting on the particle should always be proportional to the angular displacement of the particle and directed towards the equilibrium position.

Τ ∝ θ or α ∝ θ

Where,

  • Τ – Torque
  • α angular acceleration
  • θ – angular displacement