Laws of Motion — Important Questions

Walking on the ground, Recoil of a gun when fired, A book resting on a table, Rocket propulsion in space

Newton's third law states that for every action, there is an equal and opposite reaction. Walking involves foot pushing ground (action) and ground pushing foot (reaction). Gun recoil, book-table forces, and rocket thrust are all action-reaction pairs.

True

Newton's first law states that a body continues in its state of rest or uniform motion unless acted upon by an external force. For constant velocity, acceleration is zero, so net force must be zero.

Total momentum, Total kinetic energy

In elastic collisions, both total momentum and total kinetic energy are conserved. However, individual momenta and kinetic energies of objects can change during the collision.

10 N⋅s

Impulse = Force × time = F × t = 50 N × 0.2 s = 10 N⋅s. Impulse is also equal to change in momentum of the body.