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QJEEM24Phd991: JEE Main 2024 Physics - Class 11 JEEM24Phd991 Solution: A light string passing over a smooth light pulley connects two…

A light string passing over a smooth light pulley connects two blocks of masses m1m_1 and m2(m_2\left(\right. where \left.m_2>m_1\right) . If the acceleration of the system is g2\frac{g}{\sqrt{2}} , then the ratio of the masses m1m2\frac{m_1}{m_2} is:

Multiple Choice Options

  • A 1+55−1\frac{1+\sqrt{5}}{\sqrt{5}-1}
  • B 3+12−1\frac{\sqrt{3}+1}{\sqrt{2}-1}
  • C 2−12+1\frac{\sqrt{2}-1}{\sqrt{2}+1}
  • D 1+52−1\frac{1+\sqrt{5}}{\sqrt{2}-1}

Step-by-Step Verified Solution

Given that the acceleration of the system is g2\frac{g}{\sqrt{2}} , let's analyze the forces acting on both masses to find the ratio m1m2\frac{m_1}{m_2} .

The tension force in the string is equal for both masses since the pulley and string are light and smooth. Assuming the pulley only changes the direction of the tension force without affecting its magnitude, we can analyze the forces in the vertical direction for both masses.

The net force acting on m1m_1 (towards the pulley) would be the tension TT minus its weight component in the direction of motion, which we will assume is m1gm_1g , and for m2m_2 , it would be its weight component in the direction of motion, which we can assume is m2gm_2g minus the tension TT . Given that m2m_2 is moving downwards and m1m_1 is moving upwards, and considering that m_2>m_1 , the acceleration aa of both masses will be the same and can be described as:

For m1m_1 :

T−m1g=m1aT - m_1g = m_1a

For m2m_2 :

m2g−T=m2am_2g - T = m_2a

Adding these equations to eliminate TT gives:

m2g−m1g=m1a+m2am_2g - m_1g = m_1a + m_2a

Given that the acceleration aa of the system is g2\frac{g}{\sqrt{2}} , we can substitute aa with g2\frac{g}{\sqrt{2}} in the equation:

m2g−m1g=m1(g2)+m2(g2)m_2g - m_1g = m_1\left(\frac{g}{\sqrt{2}}\right) + m_2\left(\frac{g}{\sqrt{2}}\right)

Simplifying and factoring out gg , we get:

m2−m1=m12+m22m_2 - m_1 = \frac{m_1}{\sqrt{2}} + \frac{m_2}{\sqrt{2}}

Multiplying every term by 2\sqrt{2} to clear the denominator, we get:

2(m2−m1)=m1+m2\sqrt{2}(m_2 - m_1) = m_1 + m_2

Rearranging the terms to isolate the masses on one side, we obtain:

2m2−m2=m1(2+1)\sqrt{2}m_2 - m_2 = m_1(\sqrt{2} + 1)

This simplifies to:

m2(2−1)=m1(2+1)m_2(\sqrt{2} - 1) = m_1(\sqrt{2} + 1)

Hence, the ratio m1m2\frac{m_1}{m_2} is:

m1m2=2−12+1\frac{m_1}{m_2} = \frac{\sqrt{2} - 1}{\sqrt{2} + 1}

This corresponds to Option C 2−12+1\frac{\sqrt{2}-1}{\sqrt{2}+1} .

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