The formula of ferrocene is

The radius of the circle $r = 12 \cos \theta + 5 \sin \theta$ is

In the given figure,a ring of mass $m$ is kept on a horizontal surface,while a body of equal mass $m$ is attached through a string wound on the ring. When the system is released,the ring rolls without slipping. Consider the following statements and choose the correct option.
$(i)$ Acceleration of the centre of mass of the ring is $g/3$.
$(ii)$ Acceleration of the hanging particle is $2g/3$.
$(iii)$ Frictional force (on the ring) acts along the forward direction.
$(iv)$ Frictional force (on the ring) acts along the backward direction.

$A$ body,thrown upwards with some velocity,reaches a maximum height of $50 \ m$. Another body with double the mass thrown up with double the initial velocity will reach a maximum height of $.......... \ m$.

$A$ charge $Q$ is enclosed by a Gaussian spherical surface of radius $R$. If the radius is doubled,then the outward electric flux will

Eight different letters of an alphabet are given. Words of four letters from these are formed. The number of such words with at least one letter repeated is :