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

In the figure shown, a balloon is pressed against a wall. It is in equilibrium and maximum compresed state.$\vec F_1\,=$ force of balloon on hand of man $;$  $\vec F_2\,=$  force of balloon on wall $;$  $\vec F_3\,=$ friction $;$ $\vec F_4=$  weight of balloon. Choose the correct statement.

A man is pulling on a rope attached to a block on a smooth horizontal table. The tension in the rope will be the same at all points

When a body is stationary

Give the magnitude and direction of the net force acting on

$(a)$ a drop of rain falling down with a constant speed,

$(b)$ a cork of mass $10\; g$ floating on water,

$(c)$ a kite skillfully held stationary in the sky,

$(d)$ a car moving with a constant velocity of $30\; km/h$ on a rough road,

$(e)$ a high-speed electron in space far from all material objects, and free of electric and magnetic fields.