A ball is projected upwards from the top of a tower with a velocity of $50\, ms^{-1}$  making an angle of $30^o$ with the horizontal. The height of the tower is $70\, m$. After how  many seconds from the instant of throwing will the ball reach the ground ?.......$s$

A particle of mass $m$ is at rest at the origin at time $t = 0$. It is subjected to a force $F(t) = F_0e^{-bt}$ in the $x$ direction. Its speed $v (t)$ is depicted by which of the following curves?

The equation of a projectile is $y =\sqrt{3} x -\frac{ gx ^2}{2}$ the angle of projection is

The velocity at the maximum height of a projectile is $\frac{\sqrt{3}}{2}$ times its initial velocity of projection $(u)$. Its range on the horizontal plane is .............

The horizontal range and maximum height attained by a projectile are $R$ and $H$, respectively. If a constant horizontal acceleration $a=g / 4$ is imparted to the projectile due to wind, then its horizontal range and maximum height will be

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