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4.1 , newtons laws of motion — Physics STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 SciencePhysics4.1 , newtons laws of motion1 Mark
MCQ
In the arrangement shown, the $2\, kg$ block is held to keep the system at rest. The  string and pulley are ideal. When the $2\, kg$ block is set free, by what amount the  tension in the string changes? $[ g = 10\, m/s^2]$
  • A
    Increase of $12\, N$
  • ✓
    Decrease of $12\, N$
  • C
    Increase of $18\, N$
  • D
    Decrease of $18\, N$
✓

Answer

Correct option: B.
Decrease of $12\, N$
b
$\mathrm{T}_{1}=3 \mathrm{g}=3 \times 10=30 \mathrm{N}$

$a=\frac{3 g-2 g \sin 30^{\circ}}{3+2}$

$=\frac{\left(3-2 \times \frac{1}{2}\right) \times 10}{5}=2 \times 2=4 \mathrm{m} / \mathrm{s}^{2}$

$\mathrm{T}_{2}=3(\mathrm{g}-\mathrm{a})$

$=3(10-4)=18 \mathrm{N}$

$\therefore$ change $\Delta \mathrm{T} \Rightarrow \mathrm{T}_{2}-\mathrm{T}_{1}=18-30=-12 \mathrm{N}$

$\Delta \mathrm{T}=12 \mathrm{N}(\text { decrease })$

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