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A rod of mass m and length l in placed ...

A rod of mass m and length l in placed on a smooth table. An another particle of same mass m strikes the rod with velocity `v_(0)` in a direction perpendicular to the rod at distance `x( lt l//2)` from its centre . Particle sticks to the end. Let `omega` be the angular speed of system after collision , then
As x is increased from 0 to l/2 , the angular speed `omega`.

A

will continuously increase

B

will continuously decrease

C

will first increase and then decrease

D

will first increase and then decrease

Text Solution

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The correct Answer is:
To solve the problem, we will analyze the situation using the principles of conservation of angular momentum and the moment of inertia. ### Step-by-Step Solution: 1. **Understanding the System**: - We have a rod of mass \( m \) and length \( l \) placed on a smooth table. - A particle of mass \( m \) strikes the rod perpendicularly at a distance \( x \) from the center of the rod. - The particle sticks to the end of the rod after the collision. 2. **Initial Angular Momentum**: - The initial linear momentum of the particle before the collision is \( mv_0 \). - The distance from the center of the rod to the point of impact is \( x \). - Therefore, the initial angular momentum \( L_i \) about the center of the rod is given by: \[ L_i = mv_0 \cdot x \] 3. **Final Angular Momentum**: - After the collision, the system (rod + particle) will rotate about the center of mass. - Let \( \omega \) be the angular speed of the system after the collision. - The moment of inertia \( I \) of the rod about its center is: \[ I_{\text{rod}} = \frac{1}{3} ml^2 \] - The moment of inertia of the particle (considered as a point mass at a distance \( \frac{l}{2} \) from the center) is: \[ I_{\text{particle}} = m \left(\frac{l}{2}\right)^2 = \frac{ml^2}{4} \] - The total moment of inertia \( I_f \) of the system after the collision is: \[ I_f = I_{\text{rod}} + I_{\text{particle}} = \frac{1}{3} ml^2 + \frac{ml^2}{4} \] - To combine these, we find a common denominator (12): \[ I_f = \frac{4ml^2}{12} + \frac{3ml^2}{12} = \frac{7ml^2}{12} \] 4. **Applying Conservation of Angular Momentum**: - According to the conservation of angular momentum: \[ L_i = L_f \] - Therefore: \[ mv_0 \cdot x = I_f \cdot \omega \] - Substituting \( I_f \): \[ mv_0 \cdot x = \frac{7ml^2}{12} \cdot \omega \] - Canceling \( m \) from both sides: \[ v_0 \cdot x = \frac{7l^2}{12} \cdot \omega \] - Solving for \( \omega \): \[ \omega = \frac{12v_0 \cdot x}{7l^2} \] 5. **Analyzing \( \omega \) as \( x \) varies**: - As \( x \) increases from 0 to \( \frac{l}{2} \): - When \( x = 0 \): \[ \omega = 0 \] - When \( x = \frac{l}{4} \): \[ \omega = \frac{12v_0 \cdot \frac{l}{4}}{7l^2} = \frac{3v_0}{7l} \] - When \( x = \frac{l}{2} \): \[ \omega = \frac{12v_0 \cdot \frac{l}{2}}{7l^2} = \frac{6v_0}{7l} \] - Since \( \frac{3v_0}{7l} < \frac{6v_0}{7l} \), we conclude that \( \omega \) increases as \( x \) increases from 0 to \( \frac{l}{2} \). ### Conclusion: As \( x \) increases from 0 to \( \frac{l}{2} \), the angular speed \( \omega \) of the system increases.
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