Friction and Surface Area of the Object

Q. A block of unknown mass is at rest on a rough horizontal surface. A force $F$ is applied to the block. The graph in the figure shows the acceleration of the block w.r.t the applied force.
The mass of the block and coefficient of friction are $(g=10{\text{m/s}}^2)$

1. $2\text{kg},0.1$
2. $2\text{kg},0.2$
3. $1\text{kg},0.1$
4. can't be determined

Q. Which of the following statements is false about static friction?

1. It is a self-adjusting force
2. It depends on the external force applied on the body
3. It depends on the area of contact
4. It depends on the surfaces of contact.

Q. A cubical wooden box of side $L$ is placed on a horizontal rough surface and the coefficient of static friction between them is $\mu$. Another cubical box of same wood but of length $2L$ is placed on the same surface. Then the coefficient of static friction is

1. $8\mu$
2. $4\mu$
3. $2\mu$
4. $\mu$

Q. A body of mass $10\text{kg}$ is kept on a rough horizontal surface. A force of $50\text{N}$ is required to just move the body. If the body is cut into two equal parts and placed one over the other, find the force required to just move the body.

1. $10\text{N}$
2. $25\text{N}$
3. $50\text{N}$
4. $100\text{N}$