A $60\, kg$ body is pushed with just enough force to start it moving across a floor and the same force continues to act afterwards. The coefficient of static friction and sliding friction are $0.5$ and $0.4$ respectively. The acceleration of the body is  ........ $m/{s^2}$

A body of $10\, kg$ is acted by a force of $129.4\, N$ if $g = 9.8\,m/{\sec ^2}$. The acceleration of the block is $10\,m/{s^2}$. What is the coefficient of kinetic friction

A small block of mass $m$ is projected horizontally with speed $u$ where friction coefficient between block and plane is given by $\mu = cx$, where $x$ is displacement of the block on plane. Find maximum distance covered by the block 

A child weighing $25 \,kg$ slides down a rope hanging from a branch of a tall tree. If the force of friction acting against him is $200 \,N$, the acceleration of child is ........... $m / s^2$ $\left(g=10 \,m / s ^2\right)$

A bullet of mass $0.1\,kg$ moving horizontally with speed $400\,ms ^{-1}$ hits a wooden block of mass $3.9\,kg$ kept on a horizontal rough surface. The bullet gets embedded into the block and moves $20\,m$ before coming to rest. The coefficient of friction between the block and the surface is $........$ $\left(\text { Given } g=10 \,ms ^2\right. \text { ) }$

A block of mass $4\, kg$ rests on an inclined plane. The inclination of the plane is gradually increased. it is found that when the inclination is $3$ in $5\left( {\sin \theta  = \frac{3}{5}} \right)$, the block just begins to slide down the plane. The coefficient of friction between the block and the plane is