A block of $\sqrt{3}\,kg$ is attached to a string whose other end is attached to the wall. An unknown force $F$ is applied so that the string makes an angle of $30^{\circ}$ with the wall. The tension $T$ is $...........\,N$ :(Given $g =10\,ms ^{-2}$ )

A jet of liquid of cross-sectional area $'a'$ strikes a wall making angle $\theta $ with wall. The water strikes with the wall with velocity $v$ and rebounds elastically. If density of liquid be $\rho $, the normal force on the wall is

A pebble of mass $0.05\; kg$ is thrown vertically upwards. Give the direction and magnitude of the net force on the pebble,

$(a)$ during its upward motion,

$(b)$ during its downward motion,

$(c)$ at the highest point where it is momentarily at rest.

Do your answers change if the pebble was thrown at an angle of $45^o$ with the horizontal direction? Ignore air resistance.

In Newtonian mechanics which parameter apply external force ?

A boy is hanging from branch of a tree as shown. Angle between his arm, for tension to be maximum in arms must be ............ $^o$