Two particles $P$ and $Q$ start from the origin and execute Simple Harmonic Motion along the $X$-axis with the same amplitude but with periods $3 \ s$ and $6 \ s$ respectively. The ratio of the velocities of $P$ and $Q$ when they meet is

Two identical blocks $A$ and $B$,each of mass $m$,are placed on a smooth horizontal surface and are connected by a light spring of length $L$ and force constant $k$. $A$ third identical block $C$ of mass $m$ moves along the line joining $A$ and $B$ with velocity $v$ and collides with block $A$. The maximum compression in the spring is:

If $a \neq 0, b \neq 0, c \neq 0, a \times b = 0$ and $b \times c = 0$, then $a \times c$ is equal to

When the same quantity of electricity is passed through aqueous $AgNO_3$ and $H_2SO_4$ solutions connected in series,$5.04 \times 10^{-2} \ g$ of $H_2$ is liberated. What is the mass of silver (in grams) deposited? (Eq. wts. of hydrogen $= 1.008$,silver $= 108$)

The angle between the lines whose direction cosines are given by the equations $l^2+m^2-n^2=0$ and $l+m+n=0$ is