The restoring force of a spring with a block attached to the free end of the spring is represented by

Two persons are holding a rope of negligible weight tightly at its ends so that it is horizontal. A $15\, kg$ weight is attached to the rope at the mid-point, which now no longer remains horizontal. The minimum tension required to completely straighten the rope is

Two objects $A$ and $B$ each of mass $m$ are connected by a light inextensible string. They are restricted to move on a frictionless ring of radius $R$ in a vertical plane (as shown in fig). The objects are released from rest at the position shown. Then, the tension in the cord just after release is

A rope of length $10\, m$ and linear density $0.5\, kg/m$ is lying lengthwise on a smooth horizontal floor. It is pulled by a force of $25\, N$. The tension in the rope at a point $8\, m$ away from the point of application is ....... $N$

There are four forces acting at a point $P$ produced by strings as shown in figure. Which is at rest ? Find the forces $F_1$ and $F_2$.

In a hydrogen atom, the distance between the electron and proton is $2.5 \times {10^{ - 11}}\,m$. The electrical force of attraction between them will be