Learn

Saturday, 31 October

JEE Main 2021 · PhysicsMultiple choiceDiagram basedMediumMulti-step

JEE Main 16 March 2021, Shift 2, Physics Q14

Question 14 of 90 in this shift, Physics question 14 of 30, Section A.

A large block of wood of mass M = 5.99 kg is hanging from two long massless cords. A bullet of mass m = 10 g is fired into the block and gets embedded in it. The (block + bullet) then swing upwards, their centre of mass rising a vertical distance h = 9.8 cm before the (block + bullet) pendulum comes momentarily to rest at the end of its arc. The speed of the bullet just before collision is : (take g=9.8 ms−2g=9.8\ \mathrm{ms^{-2}})

The figure, in words

Ballistic pendulum: block of mass M hung from two long cords; bullet of mass m with velocity v fired horizontally into the block; dashed position shows block raised by vertical height h.
  1. (1)811.4 m/s
  2. (2)821.4 m/s
  3. (3)831.4 m/sOfficial answer
  4. (4)841.4 m/s

Official answer

Option 3

NTA final key.

Chapter
Work, Energy and Power
Topic
Collisions
Idea tested
Ballistic Pendulum

Same idea in other shifts

Asked 3× in all
  1. 1 Feb 2024, Shift 1 · Q35A simple pendulum of length 1 m has a wooden bob of mass 1 kg. It is struck by a bullet of mass 10−210^{-2} kg moving with a speed of…MediumSingle correct
  2. 27 Jun 2022, Shift 1 · Q60A pendulum of length 2 m consists of a wooden bob of mass 50 g. A bullet of mass 75 g is fired towards the stationary bob with a speed…MediumNumerical value

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.