A metal block is resting on a rough wooden surface. A horizontal force applied to the block is increased uniformly. Which of the following curves correctly represents velocity of the block ?

A block weighs $W$ is held against a vertical wall by applying a horizontal force $F$. The minimum value of $F$ needed to hold the block is $[\mu < 1]$

A $1.0 kg$ block of wood sits on top of an identical block of wood, which sits on top of a flat level table made of plastic. The coefficient of static friction between the wood surfaces is $\mu_1$, and the coefficient of static friction between the wood and plastic is $\mu_2$. Ahorizontal force $F$ is applied to the top block only, and this force is increased until the top block starts to move. The bottom block will move with the top block if and only if

Calculate the maximum acceleration (in $m s ^{-2}$) of a moving car so that a body lying on the floor of the car remains stationary. The coefficient of static friction between the body and the floor is $0.15$ $\left( g =10 m s ^{-2}\right)$.

A horizontal force $12 \,N$ pushes a block weighing $1/2\, kg$ against a vertical wall.  The  coefficient of static friction between the wall and the block is $0.5$ and the coefficient of  kinetic friction is $0.35.$ Assuming that the block is not moving  initially. Which one of the following choices is correct (Take $g = 10 \,m/s^2$)

A body takes $1\frac{1}{3}$ times as much time to slide down a rough identical but smooth inclined plane. If the angle of inclined plane is $45^o$, the coefficient of friction is