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Screenshot_2019-01-21-11-01-29-165_com.android.chrome.png A man of mass 80 Kg stand on a blank of mass 40 Kg . The block is lying on smooth horizonatl floor . Initially both are at rest . The man starts walking on the blank towards north and stops after moving a distance 6m on the blank . The plank will move

Answers (1)

@Shubham

If External Force = 0 -

\vec{P}_{total} = constant

- wherein

i.e. if no external force is acting on the system, net momentum of the system remains constant.

 

 As 

F_{ext} = 0 \\\\ so \: \: \vec a_{cm}= 0 \: \: \: \vec v_{cm}= const =0 \\\\ \vec v_{cm}=\frac{m_1\vec v_1+m_2\vec v_2}{m_1+m_2}=0 \\\\ or \: \: m_1v_1+m_2v_2= 0 \\m_1\frac{dx_1}{dt}+m_2\frac{dx_2}{dt}=0\\\\or\: \: m_1\vec x_1+ m_2 \vec x_2 = 0

x_1 = (6-x) \\x_2 = -x \\\\ m_1 (6-x) - m_2x = 0 \\\\\8 0(6-x ) = 40 x\\\\x = 4m , south 

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Safeer PP

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