Which one of the following statements is correct

What is the acceleration of the block and trolley system shown in a Figure, if the coefficient of kinetic friction between the trolley and the surface is $0.04$? What is the tension in the string ? (Take $g = 10\; m s^{-2}$). Neglect the mass of the string.

A fireman of mass $60\, kg$ slides down a pole. He is pressing the pole with a force of $600 \,N$. The coefficient of friction between the hands and the pole is $0.5$, with what acceleration will the fireman slide down ........ $m/s^2$

An insect crawls up a hemispherical surface very slowly. The coefficient of friction between the insect and the surface is $1/3$. If the line joining the centre of the hemispherical surface to the insect makes an angle $\alpha $ with the vertical, the maximum possible value of $\alpha $ so that the insect does not slip is given by

$STATEMENT-1$ It is easier to pull a heavy object than to push it on a level ground. and

$STATEMENT-2$ The magnitude of frictional force depends on the nature of the two surfaces in contact.

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 $........$ $\left(\text { Given } g=10 \,ms ^2\right. \text { ) }$