$A$ force of $98 \, N$ is required to just start moving a body of mass $100 \, kg$ over ice. The coefficient of static friction is

$A$ body of mass $4\, kg$ is at rest on a horizontal table. The coefficient of friction between the body and the table is $0.2$. $A$ horizontal force of $6\, N$ is applied on the body. The acceleration of the body is .......... $m/s^2$.

$A$ block of $1\, kg$ is stopped against a wall by applying a force $F$ perpendicular to the wall. If $\mu = 0.2$,then the minimum value of $F$ will be ....... $N$.

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

If ${\mu _s}$,${\mu _k}$,and ${\mu _r}$ are coefficients of static friction,sliding (kinetic) friction,and rolling friction respectively,then:

Is it possible to jump off a perfectly smooth surface? Why?