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JEE Main 2008 (AIEEE) · Graphs of Motion

Graphs of Motion question from JEE Main 2008 (AIEEE)

Q34JEE Main 2008 · AIEEEMedium

Graphs of Motion

A body is at rest at x=0.x = 0. At t=0,t = 0, it starts moving in the positive xx-direction with a constant acceleration. At the same instant another body passes through x=0x = 0 moving in the positive xx direction with a constant speed. The position of the first body is given by x1(t)x_1(t) after time ’t’;\text{'}t\text{'}; and that of the second body by x2(t)x_2(t) after the same time interval. Which of the following graphs correctly describes (x1−x2)(x_1 - x_2) as a function of time ’t’\text{'}t\text{'}?

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Answer: (b)

x1 - x2tO2u/a
  1. x1=12at2x_1 = \frac{1}{2}at^2, x2=utx_2 = ut, so x1−x2=12at2−utx_1 - x_2 = \frac{1}{2}at^2 - ut.
  2. This is an upward parabola through the origin: negative for 0<t<2ua0 < t < \frac{2u}{a}, zero at t=2uat = \frac{2u}{a}, then positive and rising.
  3. So the answer is (b).
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