Laws of Motion — Maharashtra (SSC) Class 9 Science Solutions (Free)

Newton's 1st law: A body at rest remains at rest, and a body in motion remains in uniform motion unless an external force acts on it. Example: A passenger in a moving bus leans backward when the bus suddenly stops because their body tends to continue moving forward due to inertia.

Using Newton's 2nd law: F = ma Step 1: Given F = 10 N, m = 2 kg Step 2: a = F/m = 10/2 = 5 m/s² Acceleration = 5 m/s²

Momentum (p) = mass × velocity = mv (unit: kg·m/s). Law of conservation: Total momentum of a system remains constant if no external force acts on it. Example: In a collision between two balls, momentum before = momentum after if no friction/external forces.

Step 1: Take one direction as positive. m₁ = 3 kg, v₁ = 4 m/s; m₂ = 2 kg, v₂ = -6 m/s Step 2: p₁ = 3 × 4 = 12 kg·m/s; p₂ = 2 × (-6) = -12 kg·m/s Step 3: Total momentum = 12 + (-12) = 0 kg·m/s

Newton's 3rd law: For every action, there is an equal and opposite reaction. Example: When you push a wall, the wall pushes you back with equal force. Both forces act on different bodies, are equal in magnitude, opposite in direction, and occur simultaneously.