Doubtclip is an AI tutor that turns any homework or exam doubt into a step-by-step whiteboard video lesson with diagrams, formulas, and voice explanation.

Which subjects and exams does it support?

It supports Physics, Chemistry, Mathematics/Calculus and related STEM doubts for school boards, JEE, NEET, and global high-school / undergrad practice.

How do I get a video solution?

Upload a photo of the question or paste the text, sign in, and Doubtclip generates a whiteboard-style explanation video you can watch and share.

Is Doubtclip available worldwide?

Yes. Doubtclip is a web app for students globally. Lessons are available in English and Hinglish.

Mechanical Properties of Solids

JEE Main level, single correct, medium

13 of 118

Question 13 of 118

A metal string $A$ is suspended from a rigid support and its free end is attached to a block of mass $M$ . Second block having mass $2M$ is suspended at the bottom of the first block using a string $B$ . The area of cross sections of strings $A$ and $B$ are same. The ratio of lengths of strings of $A$ to $B$ is $2$ and the ratio of their Young's moduli $(Y_A/Y_B)$ is $0.5$ . The ratio of elongations in $A$ to $B$ is ______.

Show answer and solution

Answer: (D) $6$

Tension in string

B

is due to the block of mass

2M

T_B = 2Mg

Tension in string

A

is due to both blocks of mass

M

and

2M

T_A = Mg + 2Mg = 3Mg

The elongation in a string is given by Hooke's law as

\Delta L = \dfrac{TL}{AY}

.

The ratio of elongations in string

A

to string

B

is:

\dfrac{\Delta L_A}{\Delta L_B} = \left(\dfrac{T_A}{T_B}\right) \left(\dfrac{L_A}{L_B}\right) \left(\dfrac{A_B}{A_A}\right) \left(\dfrac{Y_B}{Y_A}\right)

Given that

\dfrac{L_A}{L_B} = 2

\dfrac{A_B}{A_A} = 1

, and

\dfrac{Y_A}{Y_B} = 0.5 \Rightarrow \dfrac{Y_B}{Y_A} = 2

.

Substituting the values into the ratio equation:

\dfrac{\Delta L_A}{\Delta L_B} = \left(\dfrac{3Mg}{2Mg}\right) \times (2) \times (1) \times (2)

\dfrac{\Delta L_A}{\Delta L_B} = \dfrac{3}{2} \times 4 = 6

Answer:

6

JEE Main question paper PDF

Open a shift to read the full paper on this page, or download it.

JEE Main 2025 Apr 2 Shift 1 question paper

Open Download PDF

Opening paper…

Explain it as a whiteboard videoStep-by-step, in Hinglish or English. Your first video needs no login.Solved it on paper but got it wrong?Upload a photo of your working. Mistake Doctor marks the exact line that broke.

See it move: Elasticity: stress, strain and Young’s modulus simulationDrag the sliders and watch the numbers in this question change.

More Physics practice

JEE Main Physics practice question on Mechanical Properties of Solids (Young’s Modulus and Breaking Stres), with the answer and a step-by-step solution. Scan a question from your own book or paper to get a whiteboard video.