Topic: Newton's laws, force and inertia, momentum, impulse· Laws of Motion

Two blocks A and B of masses 3m and m respectively are connected by a massless and inextensible string. The whole system is suspended by a massless spring as shown in figure. The magnitudes of acceleration of A and B immediately after the string is c…

Two blocks A and B of masses 3m and m respectively are connected by a massless and inextensible string. The whole system is suspended by a massless spring as shown in figure. The magnitudes of acceleration of A and B immediately after the string is cut, are respectively :

spring from ceiling holding block A (3m), with block B (m) hanging below by string

1. \(\frac g3\), g

2. g, g

3. \(\frac g3\), \(\frac g3\)

4. g, \(\frac g3\)

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Answer: 1. \(\frac g3\), g

Key idea: the spring force cannot change instantly, but the string tension vanishes at once.

Before cutting, the spring holds both blocks: spring force \(=4mg\) upward.

After cutting: block B has only gravity, so \(a_B=g\). Block A has spring force \(4mg\) up and weight \(3mg\) down, net \(mg\) up, so \(a_A=\dfrac{mg}{3m}=\dfrac g3\).

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report

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Two blocks A and B of masses 3m and m respectively are connected by a massless and inextensible string. The whole system is suspended by a massless spring as shown in figure. The magnitudes of acceleration of A and B immediately after the string is c…

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