- Home
- Standard 11
- Physics
3-2.Motion in Plane
hard
A particle is projected from the ground at an angle of $\theta $ with the horizontal with an initial speed of $u$. Time after which velocity vector of the projectile is perpendicular to the initial velocity is
A
$u /g\,\, sin\,\, \theta $
B
$u /g\,\, cos\,\, \theta $
C
$2u /g\,\, sin\,\, \theta $
D
$2u \,\, tan\,\, \theta $
Solution
$\operatorname{since}_{x} v \perp u$ or $v . u=0$
or $(u+a t) u=0$
or $u . u+(a . u) t=0$
or $u^{2}+g u t \cos \left(90^{\circ}+\theta\right)=0$
(angle between $\left.u \text { and } u \text { is } 90^{\circ}+\theta\right)$
or $u-g t \sin \theta=0$ or $t=\frac{u}{g \sin \theta}$
Standard 11
Physics
