A block of mass $m=2 \mathrm{~kg}$ is initially at rest on a horizontal surface. A horizontal force $\mathbf{F}_1=(6 \mathrm{~N}) \hat{\mathbf{i}}$ and a vertical force $\mathbf{F}_2=(10 \mathrm{~N}) \hat{\mathbf{j}}$ are then applied to the block. The coefficients of static friction and kinetic friction for the block and the surfaces are 0.4 and 0.25 , respectively. The magnitude of the frictional force acting on the block is (assume, $g=10 \mathrm{~m} / \mathrm{s}^2$ )

A block of mass 3 kg is pressed against a vertical wall by applying a force $F$ at an angle $30^{\circ}$ to the horizontal as shown in the figure. As a result, the block is prevented from falling down. If the coefficient of static friction between the block and wall is $\sqrt{3}$, then the value of $F$ is (use, $g=10 \mathrm{~m} / \mathrm{s}^2$ )

When a bullet is fired from a rifle its momentum becomes $20 \mathrm{~kg}-\mathrm{ms}^{-1}$. If the velocity of the bullet is $1000 \mathrm{~ms}^{-1}$, then what is its mass?

A block is between two surfaces as shown in the figure. Find the normal reaction at both surfaces. [Assume, $g=10 \mathrm{~m} / \mathrm{s}^2$ ]