Medium INTEGER +4 / -1 PYQ · JEE Mains 2020

The distance x covered by a particle in one dimensional motion varies with time t as
x2 = at2 + 2bt + c. If the acceleration of the particle depends on x as x–n, where n is an integer, the value of n is __________

Answer (integer) 3

Solution

x<sup>2</sup> = at<sup>2</sup> + 2bt + c .....(1) <br><br>$\Rightarrow$ 2xv = 2at + 2b .....(2) <br><br>$\Rightarrow$ v = ${{at + b} \over x}$ <br><br>differentiating (2) w.r.t. time <br><br>$\Rightarrow$ xa' + v<sup>2</sup> = a <br><br>Here a' is acceleration. <br><br>$\Rightarrow$ a'x = a - v<sup>2</sup> = a - ${\left[ {{{at + b} \over x}} \right]^2}$ <br><br>$\Rightarrow$ a'x = ${{a{x^2} - {{\left( {at + b} \right)}^2}} \over {{x^2}}}$ <br><br>$\Rightarrow$ a' = $${{a\left( {a{t^2} + 2bt + c} \right) - {{\left( {at + b} \right)}^2}} \over {{x^2}}}$$ <br><br>$\Rightarrow$ a' = ${{ac - {b^2}} \over {{x^3}}}$ <br><br>$\therefore$ a' $\propto$ ${1 \over {{x^3}}}$ $\propto$ x<sup>-3</sup> <br><br>$\therefore$ n = 3

About this question

Subject: Physics · Chapter: Kinematics · Topic: Motion in a Straight Line

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