Q1.MomentumEasy · 1m
Define momentum and give its SI unit.
Answer: Momentum is the product of mass and velocity, p = mv; its SI unit is kg·m/s.
Class 9 · Science · Important Questions
Force and Laws of Motion — Important Questions
Q2.InertiaEasy · 2m
State Newton's first law of motion and define inertia.
Answer: An object remains at rest or in uniform motion in a straight line unless acted upon by an unbalanced force. Inertia is the tendency of a body to resist a change in its state of motion; it depends on mass.
Q3.Third LawMedium · 2m
Why do action and reaction forces not cancel each other out?
Answer: Because they act on two different bodies, not on the same body, so they cannot cancel.
Q4.Second LawMedium · 3m
A force of 20 N acts on a body of mass 4 kg. Find its acceleration.
Answer: a = F/m = 20/4 = 5 m/s².
Q5.ConservationHard · 3m
State the law of conservation of momentum.
Answer: In the absence of an external unbalanced force, the total momentum of a system of bodies remains constant before and after their interaction.
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