Question

Newton has given three laws to describe the motion of objects. According to Newton's first law, when the net external force on a body is zero, then the body is either at rest or moving with constant velocity. The first law gives the definition of inertia. Inertia means resistance to change in state of rest or motion. According to Newton's second law, the rate of change of momentum of a body is directly proportional to the external applied force on the body. The second law gives the measurement of force. According to Newton's third law, For every action, there is always equal and opposite reaction.

Give the magnitude and direction of the net force acting on a stone of mass 0.1 kg.

A block of mass 15 kg is placed on a long trolley. The coefficient of static friction between the block and the trolley is 0.18. The trolley accelerates from rest with 0.5 m/s² for 20 s and then moves with uniform velocity. Discuss the motion of the block as viewed by (i) stationary observer on the ground (ii) an observer moving with the trolley.