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JEE Main 2022 (27 Jul, Shift 2) · Velocity, Momentum & Energy in Flight

Velocity, Momentum & Energy in Flight question from JEE Main 2022 (27 Jul, Shift 2)

Q14JEE Main 2022 · 27 JUL · SHIFT 2Difficult

Velocity, Momentum & Energy in Flight

A body of mass 10 kg10\text{ kg} is projected at an angle of 45∘45^\circ with the horizontal. The trajectory of the body is observed to pass through a point (20,10)(20, 10). If TT is the time of flight, then its momentum vector, at time t=T2t = \frac{T}{\sqrt{2}}, is _____________.

[Take g=10 m/s2g = 10\text{ m/s}^{2} ]

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Answer: (d)

  1. Trajectory at 45∘45^\circ: y=x−gx2u2y = x - \frac{g x^2}{u^2}. Through (20,10)(20, 10): 10=20−10×400u2⇒u=20 m/s10 = 20 - \frac{10 \times 400}{u^2} \Rightarrow u = 20\text{ m/s}
  2. ux=uy=102 m/su_x = u_y = 10\sqrt{2}\text{ m/s}, T=2uyg=22 sT = \frac{2u_y}{g} = 2\sqrt{2}\text{ s}, so t=T2=2 st = \frac{T}{\sqrt{2}} = 2\text{ s}
  3. vy=102−20v_y = 10\sqrt{2} - 20, vx=102v_x = 10\sqrt{2}
  4. p⃗=mv⃗=1002 i^+(1002−200)j^\vec p = m\vec v = 100\sqrt{2}\,\hat i + (100\sqrt{2} - 200)\hat j
  5. So the answer is (d).
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