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Gravitation question

2007 · Shift 1 · Q62
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  5. /2007 · Shift 1 · Q62

Gravitation question

2007 · Shift 1 · Q62

JEE AdvancedPhysicsGravitationMCQ+3 / −1

Some physical quantities are given in Column I and some possible SI units in which these quantities may be expressed are given in Column II. Match the physical quantities in Column I with the units in Column II and indicate your answer by darkening appropriate bubbles in the 4 ×\times× 4 matrix given in the ORS.

Column I Column II
(A) GM e_ee​ M s_ss​
G - universal gravitational constant,
M e_ee​ - mass of the earth,
M s_ss​ - mass of the Sun
(P) (volt)
(coulomb)
(metre)
(B) 3RTM{{3RT} \over M}M3RT​
R - universal gas constant,
T - absolute temperature,
M - molar mass
(Q) (kilogram)
(metre) 3^33
(second) −2^{-2}−2
(C) F2q2B2{{{F^2}} \over {{q^2}{B^2}}}q2B2F2​
F - force,
q - charge,
B - magnetic field
(R) (metre) 2^22
(second) −2^{-2}−2
(D) GMeRe{{G{M_e}} \over {{R_e}}}Re​GMe​​
G - universal gravitational constant,
M e_ee​ - mass of the earth
R e_ee​ - radius of the earth
(S) (farad)
(volt) 2^22
(kg) −1^{-1}−1

  1. A
    (A)→(P), (Q); (B)→(R), (S); (C)→(R), (S); (D)→(R), (S)
  2. B
    (A)→(P); (B)→(R), (S); (C)→(R), (S); (D)→(R)
  3. C
    (A)→(P), (Q); (B)→(S); (C)→(R), (S); (D)→(S)
  4. D
    (A)→(Q); (B)→(R), (S); (C)→(S); (D)→(R), (S)
View written solutionFree

Correct answer: A

We match each quantity in Column I with the possible SI units in Column II.


1. Given units in Column II

  • (P)(P)(P) : (volt)(coulomb)(metre)(\text{volt})(\text{coulomb})(\text{metre})(volt)(coulomb)(metre)
  • (Q)(Q)(Q) : (kilogram)(metre)3(second)−2(\text{kilogram})(\text{metre})^3(\text{second})^{-2}(kilogram)(metre)3(second)−2
  • (R)(R)(R) : (metre)2(second)−2(\text{metre})^2(\text{second})^{-2}(metre)2(second)−2
  • (S)(S)(S) : (farad)(volt)2(kg)−1(\text{farad})(\text{volt})^2(\text{kg})^{-1}(farad)(volt)2(kg)−1

Now simplify useful unit identities:

Identity 1

(volt)(coulomb)=joule=kg m2 s−2(\text{volt})(\text{coulomb}) = \text{joule} = \text{kg}\,\text{m}^2\,\text{s}^{-2}(volt)(coulomb)=joule=kgm2s−2

So,

(P)=(volt)(coulomb)(metre)=kg m3 s−2(P)=(\text{volt})(\text{coulomb})(\text{metre})=\text{kg}\,\text{m}^3\,\text{s}^{-2}(P)=(volt)(coulomb)(metre)=kgm3s−2

which is same as (Q)(Q)(Q).

Hence,

(P)≡(Q)(P)\equiv (Q)(P)≡(Q)

Identity 2

Since

1 farad=coulombvolt,1\,\text{farad} = \frac{\text{coulomb}}{\text{volt}},1farad=voltcoulomb​,

we get

(farad)(volt)2=coulomb⋅volt=joule(\text{farad})(\text{volt})^2 = \text{coulomb}\cdot \text{volt}=\text{joule}(farad)(volt)2=coulomb⋅volt=joule

Thus,

(S)=joulekg=kg m2s−2kg=m2s−2(S)=\frac{\text{joule}}{\text{kg}} = \frac{\text{kg m}^2\text{s}^{-2}}{\text{kg}}=\text{m}^2\text{s}^{-2}(S)=kgjoule​=kgkg m2s−2​=m2s−2

So,

(S)≡(R)(S)\equiv (R)(S)≡(R)

Therefore:

  • (P)(P)(P) and (Q)(Q)(Q) are equivalent.
  • (R)(R)(R) and (S)(S)(S) are equivalent.

2. Match each expression


(A) GMeGM_eGMe​

We know

[G]=N m2kg−2=m3kg−1s−2[G] = \text{N m}^2\text{kg}^{-2}=\text{m}^3\text{kg}^{-1}\text{s}^{-2}[G]=N m2kg−2=m3kg−1s−2

So,

[GMe]=(m3kg−1s−2)(kg)=m3s−2[GM_e]=\left(\text{m}^3\text{kg}^{-1}\text{s}^{-2}\right)(\text{kg})=\text{m}^3\text{s}^{-2}[GMe​]=(m3kg−1s−2)(kg)=m3s−2

But expression is actually shown as GMeMsGM_eM_sGMe​Ms​ in the table text context, and from the options it clearly must correspond to energy×\times×length type unit:

[GMeMs]=(m3kg−1s−2)(kg)(kg)=kg m3s−2[G M_e M_s] = \left(\text{m}^3\text{kg}^{-1}\text{s}^{-2}\right)(\text{kg})(\text{kg})=\text{kg m}^3\text{s}^{-2}[GMe​Ms​]=(m3kg−1s−2)(kg)(kg)=kg m3s−2

This matches (Q)(Q)(Q), and since (P)≡(Q)(P)\equiv(Q)(P)≡(Q), it also matches (P)(P)(P).

Thus,

(A)→(P),(Q)(A)\to (P),(Q)(A)→(P),(Q)

(B) 3RTM\dfrac{3RT}{M}M3RT​

Now,

  • RRR (gas constant) has unit J mol−1K−1\text{J mol}^{-1}\text{K}^{-1}J mol−1K−1
  • TTT has unit K\text{K}K
  • MMM has unit kg mol−1\text{kg mol}^{-1}kg mol−1

So,

[RTM]=J mol−1kg mol−1=Jkg=m2s−2\left[\frac{RT}{M}\right]=\frac{\text{J mol}^{-1}}{\text{kg mol}^{-1}}=\frac{\text{J}}{\text{kg}}=\text{m}^2\text{s}^{-2}[MRT​]=kg mol−1J mol−1​=kgJ​=m2s−2

Hence it matches (R)(R)(R) and therefore also (S)(S)(S).

Thus,

(B)→(R),(S)(B)\to (R),(S)(B)→(R),(S)

(C) F2q2B2\dfrac{F^2}{q^2B^2}q2B2F2​

Use magnetic force relation:

F=qvBF=qvBF=qvB

So,

FqB=v\frac{F}{qB}=vqBF​=v

Therefore,

F2q2B2=v2\frac{F^2}{q^2B^2}=v^2q2B2F2​=v2

Unit of v2v^2v2 is

m2s−2\text{m}^2\text{s}^{-2}m2s−2

So it matches (R)(R)(R) and (S)(S)(S).

Thus,

(C)→(R),(S)(C)\to (R),(S)(C)→(R),(S)

(D) GMeRe\dfrac{GM_e}{R_e}Re​GMe​​

We have

[G]=m3kg−1s−2[G]=\text{m}^3\text{kg}^{-1}\text{s}^{-2}[G]=m3kg−1s−2

Thus,

[GMeRe]=(m3kg−1s−2)(kg)m=m2s−2\left[\frac{GM_e}{R_e}\right]=\frac{(\text{m}^3\text{kg}^{-1}\text{s}^{-2})(\text{kg})}{\text{m}}=\text{m}^2\text{s}^{-2}[Re​GMe​​]=m(m3kg−1s−2)(kg)​=m2s−2

Hence it matches (R)(R)(R) and (S)(S)(S).

Thus,

(D)→(R),(S)(D)\to (R),(S)(D)→(R),(S)

3. Final matching

So the correct matching is:

  • (A)→(P),(Q)(A) \to (P),(Q)(A)→(P),(Q)
  • (B)→(R),(S)(B) \to (R),(S)(B)→(R),(S)
  • (C)→(R),(S)(C) \to (R),(S)(C)→(R),(S)
  • (D)→(R),(S)(D) \to (R),(S)(D)→(R),(S)

This corresponds to Option A.


4. Comparison with stored answer

Stored correct answer: A

Our derived answer: A

So the derived answer agrees with the stored answer.

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