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Properties of Matter question

2024 · 4 Apr · Shift 1 · Q85
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Properties of Matter question

2024 · 4 Apr · Shift 1 · Q85

JEE MainPhysicsProperties of MatterNumerical+4 / −1
An elastic spring under tension of 3 N3 \mathrm{~N}3 N has a length aaa. Its length is bbb under tension 2 N2 \mathrm{~N}2 N. For its length (3a−2b)(3 a-2 b)(3a−2b), the value of tension will be ‾\underline{\hspace{2cm}}​ N.
Numerical answer
View written solutionFree

Correct answer: 5

  1. Use Hooke’s law for the spring

For an elastic spring, length varies linearly with tension:

L=L0+TkL = L_0 + \frac{T}{k}L=L0​+kT​

where:

  • L0L_0L0​ = प्राकृतिक length of the spring,
  • TTT = tension,
  • kkk = spring constant.

So let the length under tension TTT be written as:

L=c+mTL = c + mTL=c+mT

where c=L0c=L_0c=L0​ and m=1km=\frac{1}{k}m=k1​.


  1. Form equations from given data

When tension is 3 N3\,\text{N}3N, length is aaa:

a=c+3ma = c + 3ma=c+3m

When tension is 2 N2\,\text{N}2N, length is bbb:

b=c+2mb = c + 2mb=c+2m

Subtracting,

a−b=ma-b = ma−b=m

Also,

c=b−2mc = b-2mc=b−2m


  1. Find the length corresponding to (3a−2b)(3a-2b)(3a−2b)

Compute:

3a−2b=3(c+3m)−2(c+2m)3a-2b = 3(c+3m)-2(c+2m)3a−2b=3(c+3m)−2(c+2m)

=3c+9m−2c−4m= 3c+9m-2c-4m=3c+9m−2c−4m

=c+5m= c+5m=c+5m

But length formula is:

L=c+mTL = c + mTL=c+mT

Comparing with c+5mc+5mc+5m,

T=5 NT=5\,\text{N}T=5N


  1. Final answer

The required tension is

5\boxed{5}5​


  1. Comparison with stored correct answer

Stored correct answer = 555

My derived answer = 555

So they agree.

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