NCERT Book Class 9 Science Force And Laws Of Motion Questions

FORCE AND LAWS OF MOTION

1. 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

2. 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

3. A goalkeeper in a game of football pulls his hands backwards after holding the ball shot at the goal. This enables the goal keeper to

(a) exert larger force on the ball

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

(c) increase the rate of change of momentum

(d) decrease the rate of change of momentum

4. 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

5. A truck of mass M is moved under a force F. If the truck is then loaded with an object equal to the mass of the truck and the driving force is halved, then how does the acceleration change?

6. Two friends on roller-skates are standing 5 m apart facing each other. One of them throws a ball of 2 kg towards the other, who catches it, How will this activity affect the position of the two? Explain your answer.

7. Water sprinkler used for grass lawns begins to rotate as soon as the water is supplied. Explain the principle on which it works.

8. Using second law of motion, derive the relation between force and acceleration. A bullet of 10 g strikes a sand-bag at a speed of 103 m s-1 and gets embedded after travelling 5 cm. Calculate

(i) the resistive force exerted by the sand on the bullet

(ii) the time taken by the bullet to come to rest.

9. Derive the unit of force using the second law of motion. A force of 5 N produces an acceleration of 8 m s–2 on a mass m1 and an acceleration of 24 m s–2 on a mass m2. What acceleration would the same force provide if both the masses are tied together?

10. What is momentum? Write its SI unit. Interpret force in terms of momentum. Represent the following graphically

(a) momentum versus velocity when mass is fixed.

(b) momentum versus mass when velocity is constant

Please refer to attached file for NCERT Class 9 Science Force And Laws Of Motion Questions