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NTA Abhyas 2020
Exam
NTA Abhyas
Year
2020
Subject
Physics
Chapter
Motion in Two Dimensions

NTA Abhyas 2020 · Physics · Motion in Two Dimensions

An elastic ball is dropped on a long inclined plane. If bounces,...

An elastic ball is dropped on a long inclined plane. If bounces, hits the plane again, bounces and so on. let us Label the distance between the point of the first and second hit d12{d}_{12} and the distance between the points of second and the third hit is d23{d}_{23}. find the ratio of d12/d23{d}_{12} / {d}_{23}.

An elastic ball is dropped on a long inclined plane. If bounces, hits the plane again, bounces and so on. let us Label

Options

  1. A21\dfrac{2}{1}
  2. B12\dfrac{1}{2}
  3. C41\dfrac{4}{1}
  4. D14\dfrac{1}{4}

Correct answer

B. 12\dfrac{1}{2}

Step-by-step solution

If we rotate the coordinate system so that the ramp is horizontal, then the free fall acceleration will have two components one downward ay=−gcosθ{a}_{y} = - gcos \theta and one horizontal ax=gsinθ.{a}_{x} = gsin \theta . In this frame, the initial velocity will have components given by Vy=V0cosθ{V}_{y} = {V}_{0}cos \theta & Vx=V0sinθ{V}_{x} = {V}_{0}sin \theta time for each bounce is given by tb=2Vy−ay=2V0g{t}_{b} = \dfrac{2{V}_{y}}{- ay} = \dfrac{2{V}_{0}}{g}

The horizontal displacement \Deltax=Vxt+0.5axt2\Deltax = {V}_{x}t + 0.5{a}_{x}t^{2}

given these equation

d12=V0sinθ(2V0g)+0.5gsinθ(2V0g)2{d}_{12} = {V}_{0}sin \theta\left(\dfrac{2{V}_{0}}{g}\right) + 0.5gsin \theta{\left(\dfrac{2{V}_{0}}{g}\right)}^{2}

=4V02sinθg= \dfrac{4{V}_{0}^{2}sin \theta}{g}

d13=V0sinθ(4V0g)+0.5gsinθ(4V0g)2{d}_{13} = {V}_{0}sin \theta\left(\dfrac{4{V}_{0}}{g}\right) + 0.5gsin \theta{\left(\dfrac{4{V}_{0}}{g}\right)}^{2}

=12V02sinθg= \dfrac{12{{V}_{0}}^{2}sin \theta}{g}

Since d23=d13−d12=8V02sinθg{d}_{23} = {d}_{13} - {d}_{12} = \dfrac{8{{V}_{0}}^{2}sin \theta}{g}

d12d23=12\dfrac{{d}_{12}}{{d}_{23}} = \dfrac{1}{2}
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