$A$ car is moving at a speed of $72 \, km/hr.$ The diameter of its wheels is $0.5 \, m.$ If the wheels are stopped in $20$ rotations by applying brakes,then the angular retardation produced by the brakes is ............ $rad/s^2$. (in $.5$)

$A$ particle is projected vertically upwards from $O$ with velocity $v$ and a second particle is projected at the same instant from $P$ (at a height $h$ above $O$) with velocity $v$ at an angle of projection $\theta$. The time when the distance between them is minimum is

Two balls are projected from the same point simultaneously. The first ball is projected vertically upwards with velocity $u_1$ and the second ball at an angle of projection $60^{\circ}$ to the ground level with velocity $u_2$. Both the balls reach the ground simultaneously. The ratio of their velocities $u_1 : u_2$ is

In projectile motion,the modulus of the rate of change of velocity is:

If $\alpha$ is angular acceleration,$\omega$ is angular velocity,and $a$ is the centripetal acceleration,then which of the following is true?

$A$ person sitting in an open car moving at a constant velocity throws a ball vertically up into the air. The ball falls: