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JEE Advanced 2020Paper 1
Exam
JEE Advanced
Year
2020
Paper
Paper 1
Subject
Physics
Chapter
Units and Dimensions

JEE Advanced 2020 · Paper 1 · Physics · Units and Dimensions

Sometimes it is convenient to construct a system of units so that...

Sometimes it is convenient to construct a system of units so that all quantities can be expressed in terms of only one physical quantity. In one such system, dimensions of different quantities are given in terms of a quantity XX as follows: \left[position\right] = [Xα];[speed]=[Xβ];[acceleration]=[Xp];[linearmomentum]\left[{X}^{\alpha}\right]; \left[speed\right] = \left[{X}^{\beta}\right]; \left[acceleration\right] = \left[{X}^{p}\right];\left[linearmomentum\right] = \left[{X}^{q}\right];[force]; \left[force\right] = \left[{X}^{r}\right]. Then

Options

  1. Aα+p=2β\alpha + p = 2\beta
  2. Bp+q−r=βp + q - r = \beta
  3. Cp−q+r=αp - q + r = \alpha
  4. Dp+q+r=βp + q + r = \beta

Correct answer

A. α+p=2β\alpha + p = 2\beta

Step-by-step solution

[momentumForce]=Xp−r\left[\dfrac{momentum}{Force}\right] = {X}^{p - r}

⇒[mvma]=Xp−r⇒ \left[\dfrac{mv}{ma}\right] = {X}^{p - r}

⇒[va]=Xp−r⇒ \left[\dfrac{v}{a}\right] = {X}^{p - r}

but given that va=Xβ−p\dfrac{v}{a} = {X}^{\beta - p}

So,

p−r=β−p⇒2p=β+r...(1)p - r = \beta - p ⇒ 2p = \beta + r . . . \left(1\right)

\left[\dfrac{spee{d}^{2}}{acceleration}\right] = \left[position\right] ⇒ \dfrac{{X}^{2\beta}}{{X}^{p}} = {X}^{\alpha} ⇒ 2\beta - p = \alpha ⇒ p + \alpha = 2\beta . . . \left(2\right)</p><p>and</p><p>[forcelinearmomentum]=[accelerationspeed]⇒[XrXq]=[XpXβ]⇒r−q=p−β⇒p+q−r=β...(3)</p><p>and </p><p>\left[\dfrac{force}{linearmomentum}\right] = \left[\dfrac{acceleration}{speed}\right] ⇒ \left[\dfrac{{X}^{r}}{{X}^{q}}\right] = \left[\dfrac{{X}^{p}}{{X}^{\beta}}\right] ⇒ r - q = p - \beta ⇒ p + q - r = \beta . . . \left(3\right)

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