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3.2 , motion in plane — Physics STD 11 Science — Question

Rajasthan BoardEnglish MediumSTD 11 SciencePhysics3.2 , motion in plane1 Mark
MCQ
A projectile is launched at an angle ' $\alpha$ ' with the horizontal with a velocity $20 \; ms ^{-1}$. After $10 s$, its inclination with horizontal is ' $\beta$ '. The value of $\tan \beta$ will be : $\left( g =10 \; ms ^{-2}\right)$
  • A
    $\tan \alpha+5 \sec \alpha$
  • ✓
    $\tan \alpha-5 \sec \alpha$
  • C
    $2 \tan \alpha-5 \sec \alpha$
  • D
    $2 \tan \alpha+5 \sec \alpha$
✓

Answer

Correct option: B.
$\tan \alpha-5 \sec \alpha$
b
$v_{x}=u_{x}=20 \cos \alpha$

$v_{y}=20 \sin \alpha-10 \times 10$

$\tan \beta=\frac{v_{y}}{v_{x}}=\frac{20 \sin \alpha-100}{20 \cos \alpha}$

$=\tan \alpha-5 \sec \alpha$

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