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Units and Measurements question

2002 · Shift 0 · Q167
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Units and Measurements question

2002 · Shift 0 · Q167

JEE MainPhysicsUnits and MeasurementsMCQ+4 / −1
Identify the pair whose dimensions are equal
  1. A
    torque and work
  2. B
    stress and energy
  3. C
    force and stress
  4. D
    force and work
View written solutionFree

Correct answer: A

  1. Write dimensions of each physical quantity

    • Force: F=maF = maF=ma Since [m]=M,[a]=LT−2[m] = M, \quad [a] = LT^{-2}[m]=M,[a]=LT−2 therefore, [F]=MLT−2[F] = MLT^{-2}[F]=MLT−2

    • Work: W=F×sW = F \times sW=F×s where displacement has dimension [s]=L[s] = L[s]=L. So, [W]=[F][L]=(MLT−2)(L)=ML2T−2[W] = [F][L] = (MLT^{-2})(L) = ML^2T^{-2}[W]=[F][L]=(MLT−2)(L)=ML2T−2

    • Torque: τ=F×r\tau = F \times rτ=F×r where perpendicular distance rrr has dimension LLL. Hence, [τ]=[F][L]=(MLT−2)(L)=ML2T−2[\tau] = [F][L] = (MLT^{-2})(L) = ML^2T^{-2}[τ]=[F][L]=(MLT−2)(L)=ML2T−2

    • Stress: Stress=ForceArea\text{Stress} = \frac{\text{Force}}{\text{Area}}Stress=AreaForce​ Area has dimension L2L^2L2. Thus, [Stress]=MLT−2L2=ML−1T−2[\text{Stress}] = \frac{MLT^{-2}}{L^2} = ML^{-1}T^{-2}[Stress]=L2MLT−2​=ML−1T−2

    • Energy has same dimensions as work: [E]=ML2T−2[E] = ML^2T^{-2}[E]=ML2T−2

  2. Check each option

    • A: torque and work [τ]=ML2T−2,[W]=ML2T−2[\tau] = ML^2T^{-2}, \quad [W] = ML^2T^{-2}[τ]=ML2T−2,[W]=ML2T−2 These are equal. ✅

    • B: stress and energy [Stress]=ML−1T−2,[E]=ML2T−2[\text{Stress}] = ML^{-1}T^{-2}, \quad [E] = ML^2T^{-2}[Stress]=ML−1T−2,[E]=ML2T−2 Not equal. ❌

    • C: force and stress [F]=MLT−2,[Stress]=ML−1T−2[F] = MLT^{-2}, \quad [\text{Stress}] = ML^{-1}T^{-2}[F]=MLT−2,[Stress]=ML−1T−2 Not equal. ❌

    • D: force and work [F]=MLT−2,[W]=ML2T−2[F] = MLT^{-2}, \quad [W] = ML^2T^{-2}[F]=MLT−2,[W]=ML2T−2 Not equal. ❌

  3. Final answer

    The pair having equal dimensions is: Torque and Work\boxed{\text{Torque and Work}}Torque and Work​ So, Option A is correct.

Previous

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