1 Marks short Question Answers | Chapter - 9 | Force and laws of Motion | Physics-Class 9th

Q.1. Define the term "force".




Ans. The physical quantity which changes or tends to change the state of rest or of uniform motion of a body is called "force".

Q.2. A horse continues to apply a force in order to move a cart with a constant Speed. Why ?




Ans. The force applied by the horse balances the force of friction.

Q.3.Define momentum. What is the SI unit of momentum ?




Ans. Momentum is the product of mass and velocity. Its S.I. unit is kg ms^-1.

Q.4. State Newton's first law of motion.




Ans. A body continues in its state of rest or of uniform motion in a straight line unless an external force acts on it.

Q.5.A ball is over horizontal smooth surface with a constant velocity. What type of forces acting on the ball?




Ans. Balanced forces are acting on tbe ball.

Q.6. what is the relationship between force and acceleration ?




Ans. F = m x a - where m is the mass of a body and a is acceleration.

Q.7.Why does a gun recoil back when it is fired?




Ans. The gun recoils back when it is fired to conserve linear momentum.

Q.8. State the relation between force and momentum.




Ans. Force = Rate of change of momentum or
F = (P₂ - P₁) / t

Q.9. What is the unit of impulse?




Ans. N-s

Q.10. Define one newton of force.




Ans. One newton force is the force which produces an acceleration of 1ms^-2 when applied on a body of mass 1 kg.