Learn

Saturday, 31 October

JEE Main 2020 · PhysicsMultiple choiceSingle correctHardMulti-step

JEE Main 8 January 2020, Shift 2, Physics Q3

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

A particle of mass m is dropped from a height h above the ground. At the same time another particle of the same mass is thrown vertically upwards from the ground with a speed of 2gh\sqrt{2gh}. If they collide head-on completely inelastically, the time taken for the combined mass to reach the ground, in units of hg\sqrt{\frac{h}{g}} is :
  1. (1)12\frac{1}{2}
  2. (2)32\sqrt{\frac{3}{2}}Official answer
  3. (3)34\sqrt{\frac{3}{4}}
  4. (4)12\sqrt{\frac{1}{2}}

Official answer

Option 2

NTA final key (Jan 2020).

Chapter
Work, Energy and Power
Topic
Collisions
Idea tested
Inelastic Collisions

Same idea in other shifts

Asked 7× in all
  1. 8 Apr 2023, Shift 2 · Q40A bullet of mass 0.1 kg moving horizontally with speed 400 ms−1^{-1} hits a wooden block of mass 3.9 kg kept on a horizontal rough…MediumSingle correct
  2. 10 Apr 2023, Shift 1 · Q40A particle of mass mm moving with velocity vv collides with a stationary particle of mass 2m2m. After collision, they stick together and…EasySingle correct
  3. 25 Jul 2022, Shift 2 · Q47A bag of sand of mass 9.8 kg is suspended by a rope. A bullet of 200 g travelling with speed 10 ms−1^{-1} gets embedded in it, then loss…EasySingle correct
  4. 9 Jan 2020, Shift 1 · Q3Two particles of equal mass m have respective initial velocities ui^u\hat{i} and u(i^+j^2)u\left(\frac{\hat{i}+\hat{j}}{2}\right). They collide…MediumSingle correct
  5. 9 Jan 2020, Shift 2 · Q4A particle of mass mm is projected with a speed uu from the ground at an angle θ=π3\theta = \frac{\pi}{3} w.r.t. horizontal (xx-axis).…MediumSingle correct
  6. 3 Sep 2020, Shift 2 · Q3A block of mass 1.9 kg is at rest at the edge of a table, of height 1 m. A bullet of mass 0.1 kg collides with the block and sticks to it.…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. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.