Two spherical soap bubbles of radii $r_1$ and $r_2$ in vaccum coalesce under isothermal condition.The newly formed bubble has a radius( $r$ )given by
$r_1+r_2$
$\frac{r_1+r_2}{2}$
$\frac{r_1 r_2}{r_1+r_2}$
$\sqrt{r_1^2+r_2^2}$
A radioactive element ${ }_{92}^{242} \mathrm{X}$ emits two $\alpha$-particles,one electron and two positrons.The transformed nucleus is represented by ${ }_P^{234} Y$ .The value of $P$ is
85
87
92
96
The magnetic moment of an iron bar is $M$. It is now bent in such a way that it forms an arc section of a circle subtending an angle of $60^{\circ}$ at the centre. The magnetic moment of the arc section is
$\frac{3 M}{\pi}$
$\frac{4 M}{\pi}$
$\frac{M}{\pi}$
$\frac{2 M}{\pi}$
A uniform $\operatorname{rod} A B$ is suspended from a point $P$ ,at a variable distance $x$ ,from $A$ ,as shown in figure. To make the rod horizontal,a mass'$m$'is suspended from its end $A$ .Which set of variables will give a straight line when they are plotted?
$m, x^2$
$m, \frac1{x^2}$
$m, \frac{1}{x}$
$m, x$
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