A wooden block, initially at rest on the ground, is pushed by a force which increases linearly with time t. Which of the following curve best describes acceleration of the block with time :

Concept:

Newton's Second Law: The law states that the force 
F acting on an object is equal to the mass m of the object multiplied by its acceleration a.

F = m.a

Calculation:

\(F=ma \Rightarrow a = \frac{F}{m} = \frac{kt}{m}\)

a vs t will be straight line passing through origin.

∴ The correct option is (2).