A magnet of weight $2\mathrm{N}$ is placed on a non-magnetic horizontal table of weight $20\mathrm{N}$.Another magnet of identical geometry is kept on the underside of the table top and aligned exactly with the upper magnet but with opposite polarity.The magnetic force on the lower magnet due to the upper one is thrice the weight of the lower magnet. If this magnetic force is $6\mathrm{N}$,then

A boy throws a cricket ball from the boundary to the wicket keeper. If the frictional force due to air $\left(f_a\right)$ cannot be ignored, the forces acting on the ball at the position $X$ are represented by

A rectangular frame of some mass has to be suspended symmetrically by two mass-less strings of equal length on two supports. It can be done in one of the three following ways as shown in below figures. The tension in the strings will be

A maximum of $3 \mathrm{N}$ force can be applied on a block, down the incline, that would still not move the block which is placed on a rough inclined plane as shown in the figure. The maximum external force up the inclined plane that does not move the block is $12 \mathrm{N}$. The coefficient of static friction between the block and the plane is $\left[\mathrm{Take} g=10 \mathrm{m} {\mathrm{s}}^{-2}\right]$

Two masses connected in series with two massless strings are hanging from a support as shown in the figure. Find the tension in the upper string

Two blocks $A$ and $B$ are placed one over the other on a smooth horizontal surface. The maximum horizontal force that can be applied on lower block $A$, so that $A$ and $B$ move without separation is $49 \mathrm{N}$. The coefficient of friction between $A$ and $B$ is

A $90 \mathrm{N}$ mass is hung on a rope tied between two poles as shown in the figure. The tension $T_1$ and $T_2$ in the two parts of the rope are (in $\mathrm{N}$)

The length of a metal wire is ${\ell }_1,$ when the tension in it is $T_1$ and is ${\ell }_2$ when the tension is $T_2.$ The natural length of the wire is: