Q128 / 160 · TS EAMCET 2021 (05 Aug Shift 1) · Physics

System shown in the figure is in equilibrium and at rest. The spring and string are massless, now the string is cut. The acceleration of mass 2m and m just after the string is cut will be
Figure

  • Correct answer
    A
    g2 upwards, g downwards
  • B
    g upwards, g2 downwards
  • C
    g upwards, 2g downwards
  • D
    2g upwards, g downwards

Solution

Figure
Initially, both the blocks were under equilibrium, so for mass m,
T=mg, 
and for mass 2m,
Fs=T+2mg=3mg
Now, after the string is cut, the tension in it becomes zero. Therefore, 
for m,
mg-0=ma ⇒a=g(downward)
and for 2m,
2mg+0-Fs=2mb2mg+0-3mg=2mb⇒b=-g2
i.e., g2 upward.

Hence, the correct answer is option: 'A'.

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