$A$ force acts for $20\,s$ on a body of mass $20\,kg$,starting from rest,after which the force ceases and the body travels $50\,m$ in the next $10\,s$. The value of the force is $..........\,N$.

$A$ cubical box of side $a$ sitting on a rough table-top is pushed horizontally with a gradually increasing force until the box moves. If the force is applied at a height from the table top which is greater than a critical height $H$,the box topples first. If it is applied at a height less than $H$,the box starts sliding first. Then,the coefficient of friction between the box and the table top is

$A$ spring is compressed between two toy carts of masses $m_1$ and $m_2$. When the toy carts are released,the spring exerts an equal and opposite force on each cart for the same time $t$. If the coefficient of friction $\mu$ between the ground and the carts is the same,find the ratio of the displacements of the two toy carts.

$A$ plank with a box on it at one end is gradually raised about the other end. As the angle of inclination with the horizontal reaches $30^o$,the box starts to slip and slides $4.0\, m$ down the plank in $4.0\, s$. The coefficients of static and kinetic friction between the box and the plank will be,respectively:

In the following problem,indicate the correct direction of the friction force acting on the cylinder,which is pulled on a rough surface by a constant force $F$. $A$ spool is pulled horizontally by a constant force $F$ applied below the center of mass. Which of the following diagrams correctly shows the direction of the friction force?

In which of the following cases is the contact force between $A$ and $B$ maximum? (Given: $m_A = m_B = 1 \ kg$)