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Saturday, 31 October

JEE Main 2020 · PhysicsMultiple choiceSingle correctHardMulti-step

JEE Main 3 September 2020, Shift 1, Physics Q3

Question 3 of 75 in this shift, Physics question 3 of 25.

A block of mass m = 1 kg slides with velocity vv = 6 m/s on a frictionless horizontal surface and collides with a uniform vertical rod and sticks to it as shown. The rod is pivoted about O and swings as a result of the collision making angle θ\theta before momentarily coming to rest. If the rod has mass M = 2 kg, and length ll = 1 m, the value of θ\theta is approximately : (take g = 10 m/s2^2)

The figure, in words

A block of mass m on a horizontal line moves with velocity v (arrow to the right) toward a vertical rod drawn with dashed outline, pivoted at its top end O; a dashed small block m sits at the lower end of the rod beside it. The rod (labelled M, l) is also drawn swung to the right at angle theta from the vertical, with a diamond-shaped block m at its lower end.
  1. (1)49∘49^\circ
  2. (2)55∘55^\circ
  3. (3)63∘63^\circOfficial answer
  4. (4)69∘69^\circ

Official answer

Option 3

NTA final key (Sep 2020).

Chapter
System of Particles and Rotational Motion
Topic
Angular Momentum
Idea tested
Collisions with Pinned Rigid Bodies

Same idea in other shifts

Asked 2× in all
  1. 8 Jan 2020, Shift 1 · Q4Consider a uniform rod of mass M = 4m and length ll pivoted about its centre. A mass m moving with velocity vv making angle…MediumSingle correct

Question text from the official JEE Main paper published by NTA; answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. This question needs a figure we do not reproduce; it is described in words above. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.