A block of mass $m$ is moving with a constant acceleration a on a rough plane. If the coefficient of friction between the block and ground is $\mu $, the power delivered by the external agent after a time $t$ from the beginning is equal to
$ma^2t$
$\mu mgat$
$\mu m(a + \mu g)\, gt$
$m(a + \mu g)\, at$
Static friction between two surfaces
Given in the figure are two blocks $A$ and $B$ of weight $20\, N$ and $100\, N$, respectively. These are being pressed against a wall by a force $F$ such that the system does not slide as shown. If the coefficient of friction between the blocks is $0.1$ and between block $B$ and the wall is $0.15$, the frictional force applied by the wall on block $B$ is ........ $N$
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 block of mass $2 \,kg$ is kept on the floor. The coefficient of static friction is $0.4$. If a force F of $2.5$ Newtons is applied on the block as shown in the figure, the frictional force between the block and the floor will be ........ $N$
Explain -“Static friction force opposes impending motion”.