Chapter 9. FORCE AND LAWS OF MOTION

Class 9 Science Examplar Chapter 9. FORCE AND LAWS OF MOTION Choose the correct answers :

Q1. What is the momentum of an object of mass ,moving with a velocity  ?

(A)   

(B) 

(C)   

(D)    

Ans : (C)    

Q2. The product of mass and velocity gives a physical quantity :

(A) Newton

(B) Force

(C) Inertia

(D) Momentum

Ans : (D) Momentum .

Q3. The S.I. unit of momentum is :

(A)   

(B)   

(C)  

(D)   

Ans :  (C)  

Q4. The SI unit of force is :

(A)   

(B)   

(C)  

(D)   

Ans : (B)   

Q5. Which of the following statement is not correct for an object moving along a straight path in an accelerated motion ?

(A) Its speed keeps changing

(B) Its velocity always changes

(C) It always goes away from the earth

(D) a force is always acting on it

Ans :  (C) It always goes away from the earth .

Q6. According to the third law of motion , action and reaction

(A) always act on the same body

(B) always act on different bodies in opposite directions

(C) have same magnitude and directions

(D) act on either body at normal to each other

Ans : (B) always act on different bodies in opposite directions .

Q7. A goalkeeper in a game of football pulls his hands backwards after holding the ball shot at the goal .The enable the goal keeper to :

(i) exert larger force on the ball

(ii) reduce the force exerted by the ball on hands

(iii) increase the rate of change of momentum

(v) decrease the rate of change of momentum

(A) (ii) and (iv)   

(B) (i) and (ii) 

(C) (iii) and (iv)

(D) (i) and (iii)

Ans : (A) (ii) and (iv)   . 

Q8. The inertia of an object tends to cause the object :

(A) to increase its speed

(B) to decrease its speed

(C) to resist any change in its state of motion

(D) to decelerate due to friction

Ans : (C) to resist any change in its state of motion .

Q9. A passenger in a moving train tosses a coin which falls behind him . It means that motion of  the train is :

(A) accelerated

(B) uniform

(C) retarded

(D) along circular tracks

Ans :  (A) accelerated .

Q10. An object of mass 2 kg is sliding with a constant velocity of 4 m/s on a frictionless horizontal table . The force required to keep the object moving with the same velocity is :

(A) 32 N

(B) 0 N

(C) 2 N

(D) 8 N

Ans : (B) 0 N .

Q11. Rocket works on the principle of conservation of :

(A) mass

(B) energy

(C) momentum

(D) velocity

Ans : (C) momentum .

Q12. A water tanker filled up to   of its height is moving with a uniform speed . On sudden application of the brake , the water in the tank would :

(A) move backward

(B) move forward

(C) be unaffected

(D) rise upwards

Ans : (B) move forward .

Q13. A football and a stone has same mass

(A) both have same inertia

(B) both have different momentum

(C) both have same momentum

(D) both have different inertia

Ans :  (A) both have same inertia .

Class 9 Science Examplar Chapter 9. FORCE AND LAWS OF MOTION Fill in the blanks :

Q14. The mass of an object is a measure of its  .

Ans : inertia .

Q15. of fraction always opposes motion of objects .

Ans : Force .

Q16. The  of an object is the product of its mass and velocity and has the same direction as that of the velocity .

Ans : momentum .