Question

Two blocks are connected by a spring. The combination is suspended, at rest, from a string attached to the ceiling, as shown in the figure. The string breaks suddenly. Immediately after the string breaks, what is the initial downward acceleration of the upper block of mass 2m?

• A. 0
• B. 3g/2
• C. g
• D. 2g

Answer 1

Answer: (B)

3g/2

Let $a$ is the initial downward acceleration of the upper block of mass 2m.
before breaking of string, $T=2mg+kx$

& $kx=mg$

Now, after the string is cut, the forces on the 2m block are: $2mgandkx(=mg)$

the equation of motion of the mass $2m$ is , $2ma=(2m+m)g$
$\therefore a=\frac{3g}{2}$
Ans:(B)