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3.1 vectors — Physics STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 SciencePhysics3.1 vectors1 Mark
MCQ
A body is moving under the action of two forces ${\vec F_1} = 2\hat i - 5\hat j\,;\,{\vec F_2} = 3\hat i - 4\hat j$. Its velocity will become uniform under an additional third force ${\vec F_3}$ given by
  • A
    $5\hat i - \hat j$
  • B
    $-5\hat i - \hat j$
  • C
    $5\hat i + \hat j$
  • ✓
    $-5\hat i + 9\hat j$
✓

Answer

Correct option: D.
$-5\hat i + 9\hat j$
d
For uniform velocity, acceleration is zero. Hence resultant force will be zero.

$\therefore \overrightarrow{\mathrm{F}}_{1}+\overrightarrow{\mathrm{F}}_{2}+\overrightarrow{\mathrm{F}}_{3}=0$

$(2 \hat{i}-5 \hat{j})+(3 \hat{i}-4 \hat{j})+\vec{F}_{3}=0$

or $\overrightarrow{\mathrm{F}}_{3}=(-5 \hat{\mathrm{i}}+9 \hat{\mathrm{j}})$

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