$A$ police car with a siren of frequency $8 \, kHz$ is moving with uniform velocity $36 \, km/hr$ towards a tall building which reflects the sound waves. The speed of sound in air is $320 \, m/s$. The frequency of the siren heard by the car driver is .... $kHz$.

The path of a projectile is given by the equation $y = ax - bx^2$,where $a$ and $b$ are constants and $x$ and $y$ are respectively horizontal and vertical distances of the projectile from the point of projection. The maximum height attained by the projectile and the angle of projection are respectively:

Which of the following statements is not correct regarding calcination?

$A$ metal sphere of radius $r$ and specific heat $S$ is rotated about an axis passing through its centre at a speed of $n$ rotations per second. It is suddenly stopped and $50 \%$ of its energy is used in increasing its temperature. Then,the rise in temperature of the sphere is

Continuous bleeding from an injured part of the body is due to the deficiency of:

If the sum of two unit vectors is a unit vector,what is the magnitude of their difference?