Among the forces in nature,friction can be classified into

For the given system,find the value of ${\theta _1}$ in degrees.

Five persons $A, B, C, D$ and $E$ are pulling a cart of mass $100 \, kg$ on a smooth surface and the cart is moving with an acceleration of $3 \, m/s^2$ in the east direction. When person $A$ stops pulling,it moves with an acceleration of $1 \, m/s^2$ in the west direction. When person $B$ stops pulling,it moves with an acceleration of $24 \, m/s^2$ in the north direction. The magnitude of the acceleration of the cart when only $A$ and $B$ pull the cart,keeping their directions the same as the original directions,is ............ $m/s^2$.

$A$ packet of weight $W$ dropped from a parachute strikes the ground and comes to rest with retardation equal to twice the acceleration due to gravity. The force exerted on the ground is

Block $B$ of mass $100 \ kg$ rests on a rough surface with a friction coefficient $\mu = 1/3$. $A$ rope is tied to block $B$ as shown in the figure. The maximum acceleration with which boy $A$ of mass $25 \ kg$ can climb the rope without making the block move is:

On a stationary sail-boat,air is blown at the sails from a fan attached to the boat. The boat will