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  • Help me please, - A rigid massless rod of length has two masses attached at each end as shown in the figure. The rod - Rotational Motion - JEE Main

A rigid massless rod of length 3l has two masses attached at each end as shown in the figure. The rod is pivoted at point P on the horizontal axis (see figure). When released from initial horizontal position, its instantaneous angular acceleration will be:

 

  • Option 1) (g/3l)
  • Option 2) (7g/3l) 
  • Option 3)(g/13l) 
  • Option 4)(g/2l) 

Answers (1)

best_answer

 

Torque -

\underset{\tau }{\rightarrow}= \underset{r}{\rightarrow}\times \underset{F}{\rightarrow}   

 

- wherein

This can be calculated by using either  \tau=r_{1}F\; or\; \tau=r\cdot F_{1}

r_{1} = perpendicular distance from origin to the line of force.

F_{1} = component of force perpendicular to line joining force.

 

 

 

 

Analogue of second law of motion for pure rotation -

\vec{\tau }=I\, \alpha

- wherein

Torque equation can be applied only about two point

(i) centre of motion.

(ii) point which has zero velocity/acceleration.

 

About point P

2M_{0}2L - 5M_{0}gL=Id

I = 2M_{0}(2l)^{2}+5M_{0}l^{2} = 13M_{0}l^{2}d

d= \frac{-M_{0}gl}{13M_{0}l^{2}} = -\frac{g}{13l} = \frac{g}{13l}

 

 


Option 1)

\frac{g}{3l}

Option 2)

\frac{7g}{3l}

Option 3)

\frac{g}{13l}

Option 4)

\frac{g}{2l}

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