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Units and Measurements question

2024 · 6 Apr · Shift 1 · Q65
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  5. /2024 · 6 Apr · Shift 1 · Q65

Units and Measurements question

2024 · 6 Apr · Shift 1 · Q65

JEE MainPhysicsUnits and MeasurementsMCQ+4 / −1
To find the spring constant (k)(k)(k) of a spring experimentally, a student commits 2%2 \%2% positive error in the measurement of time and 1%1 \%1% negative error in measurement of mass. The percentage error in determining value of kkk is :
  1. A
    5%
  2. B
    3%
  3. C
    1%
  4. D
    4%
View written solutionFree

Correct answer: A

  1. Relation for spring constant

For a mass-spring system, the time period is

T=2πmkT = 2\pi \sqrt{\frac{m}{k}}T=2πkm​​

Squaring both sides:

T2=4π2mkT^2 = 4\pi^2 \frac{m}{k}T2=4π2km​

So,

k=4π2mT2k = 4\pi^2 \frac{m}{T^2}k=4π2T2m​

Hence,

k∝mT2k \propto \frac{m}{T^2}k∝T2m​


  1. Use percentage error formula

For a quantity

k∝m T−2k \propto m\, T^{-2}k∝mT−2

the fractional error is

Δkk=Δmm+2ΔTT\frac{\Delta k}{k} = \frac{\Delta m}{m} + 2\frac{\Delta T}{T}kΔk​=mΔm​+2TΔT​

when taking maximum percentage error in magnitude.

Given:

  • Mass has 1% negative error ⇒\Rightarrow⇒ magnitude of error in mmm is 1%1\%1%
  • Time has 2% positive error ⇒\Rightarrow⇒ magnitude of error in TTT is 2%2\%2%

Therefore,

% error in k=1%+2(2%)=1%+4%=5%\%\text{ error in }k = 1\% + 2(2\%) = 1\% + 4\% = 5\%% error in k=1%+2(2%)=1%+4%=5%


  1. Check options
  • A: 5%5\%5% ✅
  • B: 3%3\%3%
  • C: 1%1\%1%
  • D: 4%4\%4%

So the correct option is A.


  1. Comparison with stored answer

Stored correct answer: A

My derived answer: A

They match.

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