JEE Main 2026 · 2 Apr · Shift 2 · Physics Q28

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PhysicsSingle correct+4 / -1Question 28 of 75

Two blocks of masses 2 kg and 1 kg respectively, are tied to the ends of a string which passes over a light frictionless pulley as shown in the figure below. The masses are held at rest at the same horizontal level and then released. The distance traversed by the centre of mass in 2 s is ________ m. (Take $g=10$ m/s²)

A light pulley hangs from a ceiling support; a string over it carries a 2 kg block on the left and a 1 kg block on the right, both hanging at the same height.

3.33

3.12

2.22

1.42

Answer and worked solution

Official answer: C

Atwood machine. $a=\dfrac{(2-1)g}{3}=\dfrac{10}3$ m/s². The 2 kg block moves down and the 1 kg block up.

Centre of mass. $a_\text{cm}=\dfrac{2a-1\cdot a}3=\dfrac a3=\dfrac{10}9$ m/s², downward, from rest.

Distance. $s=\frac12\cdot\frac{10}9\cdot2^2=2.22$ m.

(C)

Topics:Centre of mass Constraint motion and pulleys

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JEE Main 2026 · 2 Apr · Shift 2, Physics question 28