An object of weight w is pulled along a rough horizontal surface by a force $P$. The force of friction is $F$. Which diagram correctly shows the direction of these forces on the object?

Three blocks A, B and C of masses $4 \mathrm{kg}$, $2 \mathrm{kg}$ and $1 \mathrm{kg}$ respectively, are in contact on a frictionless surface as shown. If a force of $14 \mathrm{N}$ is applied on the $4 \mathrm{kg}$ block, then contact force between A and B is, 

A person just supports a mass of $20 \mathrm{kg}$ suspended from a rope. What is the resultant force acting on the mass? 

The velocity-time graph of a ball moving on the surface of a floor is given below.

If the mass of the ball is $200 \mathrm{g}$, then the value of force on the ball is

Study the diagram given below.

Which type (s) of forces cause (s) the spring to extend most?

A. Elastic force exerted by the spring.

B. Magnetic force acting on the iron box. 

C. Gravitational force acting on the iron box.

D. Frictional force acting between the iron box and the magnet.