Learn

Saturday, 31 October

JEE Main 2020 · PhysicsNumerical answerNumerical valueHardMulti-step

JEE Main 2 September 2020, Shift 2, Physics Q21

Question 21 of 75 in this shift, Physics question 21 of 25.

A particle of mass m is moving along the x-axis with initial velocity ui^\hat{i}. It collides elastically with a particle of mass 10 m at rest and then moves with half its initial kinetic energy (see figure). If sin⁡θ1=n sin⁡θ2\sin\theta_1 = \sqrt{n}\,\sin\theta_2 then value of n is __________.

The figure, in words

A dot labelled m at the left with an arrow along the x-axis labelled u î pointing right towards a dot labelled 10 m. After the collision point, the particle m goes up and to the right (arrow, dot labelled m at its end) making angle θ1 with a dashed horizontal line through the collision point; the particle 10 m goes down and to the right (arrow, dot labelled 10 m at its end) making angle θ2 below the dashed horizontal line.

Official answer

10.00

NTA final key (Sep 2020).

Chapter
System of Particles and Rotational Motion
Topic
Collisions
Idea tested
Oblique Collisions

Same idea in other shifts

Asked 6× in all
  1. 31 Aug 2021, Shift 1 · Q20A body of mass M moving at speed V0V_0 collides elastically with a mass 'm' at rest. After the collision, the two masses move at angles…HardSingle correct
  2. 24 Feb 2021, Shift 1 · Q23A ball with a speed of 9 m/s collides with another identical ball at rest. After the collision, the direction of each ball makes an angle…MediumNumerical value
  3. 8 Jan 2020, Shift 1 · Q22A body A, of mass m = 0.1 kg has an initial velocity of 3i^3\hat{i} ms−1^{-1}. It collides elastically with another body, B of the same…MediumNumerical value
  4. 2 Sep 2020, Shift 1 · Q3A particle of mass mm with an initial velocity ui^u\hat{i} collides perfectly elastically with a mass 3m3m at rest. It moves with a…MediumSingle correct
  5. 6 Sep 2020, Shift 2 · Q4Particle A of mass m1m_1 moving with velocity (3i^+j^) ms−1\left(\sqrt{3}\hat{i}+\hat{j}\right)\,\mathrm{ms^{-1}} collides with another particle B of…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.