Three blocks of masses ${m_1},\,{m_2}$ and ${m_3}$ are connected by massless strings as shown on a frictionless table. They are pulled with a force ${T_3} = 40\,N$. If ${m_1} = 10\,kg,\,{m_2} = 6\,kg$ and ${m_3} = 4\,kg$, the tension ${T_2}$ will be ........ $N$

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

Explain main type of force with suitable example.

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.

Two particles of mass $m$ each are tied at the ends of a light string of length $2a$ . The whole system is kept on a frictionless horizontal surface with the string held tight so that each mass is at a distance $'a'$ from the centre $P$ (as shown in the figure). Now, the mid-point of the string is pulled vertically upwards with a small but constant force $F$ . As a result, the particles move towards each other on the surface. The magnitude of acceleration, when the separation between them becomes $2x$ , is

A body of mass $m$ hangs at one end of a string of length $l$, the other end of which is fixed. It is given a horizontal velocity so that the string would just reach where it makes an angle of $60^o$ with the vertical. The tension in the string at mean position is