A small body slips, subject to the force of friction, from point $A$ to point $B$ along two curved surfaces of equal radius, first along route $1,$ then along route $2$. Friction does not depend on the speed and the coefficient of friction on both routes is the same. In which case will the body’s speed at $B$ be greater?

What is friction ? What is impending motion ?

A boy of mass $4\, kg$ is standing on a piece of wood having mass $5 \,kg$. If the coefficient of friction between the wood and the floor is $0.5,$ the maximum force that the boy can exert on the rope so that the piece of wood does not move from its place is ......$N.$(Round off to the Nearest Integer) [Take $g=10 \,ms ^{-2}$ ]

If the normal force is doubled, the coefficient of friction is

$Assertion$ : On a rainy day it is difficult to drive a car or bus at high speed.
$Reason$ : The value of coefficient of friction is lowered due to wetting of the surface

Aball of mass $m$ is thrown vertically upwards.Assume the force of air resistance has magnitude proportional to the velocity, and direction opposite to the velocity's. At the highest point, the ball's acceleration is