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Laws of Motion question

2024 · 6 Apr · Shift 1 · Q67
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  5. /2024 · 6 Apr · Shift 1 · Q67

Laws of Motion question

2024 · 6 Apr · Shift 1 · Q67

JEE MainPhysicsLaws of MotionMCQ+4 / −1
A light string passing over a smooth light pulley connects two blocks of masses m1m_1m1​ and m2(m_2\left(\right.m2​( where m2>m1)\left.m_2>m_1\right)m2​>m1​). If the acceleration of the system is g2\frac{g}{\sqrt{2}}2​g​, then the ratio of the masses m1m2\frac{m_1}{m_2}m2​m1​​ is:
  1. A
    1+55−1\frac{1+\sqrt{5}}{\sqrt{5}-1}5​−11+5​​
  2. B
    3+12−1\frac{\sqrt{3}+1}{\sqrt{2}-1}2​−13​+1​
  3. C
    2−12+1\frac{\sqrt{2}-1}{\sqrt{2}+1}2​+12​−1​
  4. D
    1+52−1\frac{1+\sqrt{5}}{\sqrt{2}-1}2​−11+5​​
View written solutionFree

Correct answer: C

  1. Identify the system

This is an Atwood machine with masses m1m_1m1​ and m2m_2m2​ connected by a light string over a smooth light pulley, with m2>m1m_2 > m_1m2​>m1​.

The acceleration of such a system is

a=(m2−m1)gm1+m2.a = \frac{(m_2-m_1)g}{m_1+m_2}.a=m1​+m2​(m2​−m1​)g​.

Given:

a=g2.a = \frac{g}{\sqrt{2}}.a=2​g​.

So,

(m2−m1)gm1+m2=g2.\frac{(m_2-m_1)g}{m_1+m_2} = \frac{g}{\sqrt{2}}.m1​+m2​(m2​−m1​)g​=2​g​.

Cancel ggg:

m2−m1m1+m2=12.\frac{m_2-m_1}{m_1+m_2} = \frac{1}{\sqrt{2}}.m1​+m2​m2​−m1​​=2​1​.


  1. Express in terms of the ratio

Let

r=m1m2.r = \frac{m_1}{m_2}.r=m2​m1​​.

Then m1=rm2m_1 = rm_2m1​=rm2​. Substitute:

m2−rm2rm2+m2=12.\frac{m_2-rm_2}{rm_2+m_2} = \frac{1}{\sqrt{2}}.rm2​+m2​m2​−rm2​​=2​1​.

1−r1+r=12.\frac{1-r}{1+r} = \frac{1}{\sqrt{2}}.1+r1−r​=2​1​.


  1. Solve for rrr

Cross-multiplying:

2(1−r)=1+r.\sqrt{2}(1-r) = 1+r.2​(1−r)=1+r.

Expand:

2−2r=1+r.\sqrt{2} - \sqrt{2}r = 1 + r.2​−2​r=1+r.

Bring rrr terms together:

2−1=r(2+1).\sqrt{2}-1 = r(\sqrt{2}+1).2​−1=r(2​+1).

Hence,

r=2−12+1.r = \frac{\sqrt{2}-1}{\sqrt{2}+1}.r=2​+12​−1​.

Therefore,

m1m2=2−12+1.\frac{m_1}{m_2} = \frac{\sqrt{2}-1}{\sqrt{2}+1}.m2​m1​​=2​+12​−1​.


  1. Match with the options

This corresponds to Option C.


  1. Compare with stored correct answer

Stored correct answer: C

Our derived answer: C

So they agree.

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