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Saturday, 31 October

JEE Main 2021 · PhysicsMultiple choiceDiagram basedMediumApplication

JEE Main 26 February 2021, Shift 2, Physics Q10

Question 10 of 90 in this shift, Physics question 10 of 30, Section A.

Two masses A and B, each of mass M are fixed together by a massless spring. A force acts on the mass B as shown in figure. If the mass A starts moving away from mass B with acceleration ‘a’, then the acceleration of mass B will be :

The figure, in words

A horizontal line with two dots, B on the left and A on the right, joined by a spring drawn between them. An arrow labelled F points to the left from the left end, at B. Labels: F, B, A.
  1. (1)MFF+Ma\frac{MF}{F + Ma}
  2. (2)F+MaM\frac{F + Ma}{M}
  3. (3)Ma−FM\frac{Ma - F}{M}
  4. (4)F−MaM\frac{F - Ma}{M}Official answer

Official answer

Option 4

NTA final key.

Chapter
Laws of Motion
Topic
Newton's Laws of Motion
Idea tested
F=ma for Single Body

Same idea in other shifts

Asked 9× in all
  1. 4 Apr 2026, Shift 2 · Q28At t=0t=0, a body of mass 100 g starts moving under the influence of a force (5i^+10j^)\left(5\hat i+10\hat j\right) N. After 2 s its position is…EasySingle correct
  2. 7 Apr 2025, Shift 2 · Q28An object with mass 500 g moves along xx-axis with speed v=4xv=4\sqrt{x} m/s. The force acting on the object is :MediumSingle correct
  3. 1 Feb 2024, Shift 2 · Q34A body of mass 44 kg experiences two forces F⃗1=5i^+8j^+7k^\vec{F}_1 = 5\hat{i} + 8\hat{j} + 7\hat{k} and…EasySingle correct
  4. 8 Apr 2023, Shift 1 · Q36At any instant the velocity of a particle of mass 500 g500\ \mathrm{g} is (2ti^+3t2j^) ms−1(2t\hat{i}+3t^2\hat{j})\ \mathrm{ms^{-1}}. If the force acting on…EasySingle correct
  5. 25 Jun 2022, Shift 1 · Q60A force on an object of mass 100 g is (10 i^+5j^)(10\,\hat{i}+5\hat{j}) N. The position of that object at t = 2 s is (ai^+bj^)(a\hat{i}+b\hat{j}) m after…EasyNumerical value
  6. 26 Feb 2021, Shift 1 · Q22A boy pushes a box of mass 2 kg with a force F⃗=(20i^+10j^)\vec{F}=\left(20\hat{i}+10\hat{j}\right) N on a frictionless surface. If the box was…EasyNumerical value
  7. 25 Jul 2021, Shift 2 · Q6A force F⃗=(40i^+10j^)\vec{F} = (40\hat{i} + 10\hat{j})N acts on a body of mass 5 kg. If the body starts from rest, its position vector r⃗\vec{r} at…EasySingle correct
  8. 16 Mar 2021, Shift 2 · Q23A body of mass 2 kg moves under a force of (2i^+3j^+5k^)(2\hat{i}+3\hat{j}+5\hat{k}) N. It starts from rest and was at the origin initially. After 4…EasyNumerical 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.