Assignment - Force & NLM, Class 9, Science PDF Download

Extra Practice Questions (Solved & Un-solved) : Force & NLM (Force and Newtons Laws of Motion), Class 9 Science
 

Match the Column :-

Single column (matrix) :-

1. Column - I                                                 Column - II

(A) Dusting of a carpet.                                   (p) Inertia of direction.

(B) Vehicles are provided with mud guards.       (q) Inertia of motion.

(C) Fan continues to rotate after switching off.  (r) Measure of inertia.

(D) Mass.                                                      (s) Inertia of rest.

2. Column - I                                               Column - II

(A) Rocket propulsion.                                   (p) Force.

(B) Agent which causes acceleration.             (q) Momentum.

(C) Product of mass and velocity.                   (r) SI unit of force.

(D) Newton.                                                 (s) Law of conservation of momentum.

Double column (matrix) :-

3. Column - I                                             Column - II

(A) Qualitative definition of force.                  (p) Galileo's law.

(B) Recoil of a gun.                                     (q) Newton's second law.

(C) Quantitative definition of force.                (r) Law of conservation of momentum.

(D) Law of inertia.                                       (s) Newton's third law.

                                                                (t) Newton's first law.

4. Column - I                                                       Column - II

(A) To every action there is an equal and                (p) Galilieo's law of inertia.

opposite reaction.

(B) A body cannot change its state of rest              (q) Newton's third law.

or of uniform motion without the help

of force.

(C) Rate of change of momentum is directly            (r) Law of conservation of momentum.

proportional to the applied force and takes

place in the direction of the force.

(D) The linear momentum of a system remains        (s) Newton's second law.

conserved in the absence of an external force          (t) Newton's first law.

Mark the statement true or false :-

1. Force may or may not produce any motion in a body.

2. Action and reaction act on the same body.

3. Impulse represents the rate of change of momentum of a body.

4. 1 N is that force which produces an acceleration of 1 ms² in a body of mass 1 g.

5. In any interaction there are always at least two forces in play.

6. The force of friction is smaller in solids than in liquids.

7. The first law of motion is also known as Gallieo's law of inertia.

Fill in the blanks :-

1. A force is an ......................... whose action can produce acceleration.

2. Inertia is of ......................... types.

3. The total ......................... contained in a body is called momentum.

4. Newton's first law gives the ......................... definition of force.

5. The rate of change of momentum is ......................... to the applied force.

6. The total effect of force is called .........................

7. Newton's second law gives the ......................... definition of force.

8. Newton's third law tells that ......................... force does not exist.

9. If no externa force acts on a system of particles then the ......................... of the system remains conserved.

10. Rocket works on the principle of .........................

ANSWER KEY

Match the Column :-

12. (A, s), (B, p), (C, q), (D, r) 13. (A, s), (B, p), (C, q), (D, r)

14. (A, p, t), (B, r, s), (C, q), (D, t) 15. (A, t), (B, p, q), (C, s), (D, r)

True & false :-

1. True 2. False 3. False 4. False

5. True 6. False 7. True

Fill in the blanks :-

1. Agent 2. Three 3. Motion 4. Qualitative

5. Directly proportional 6. Impulse 7. Quantitative

Very short answer type questions :

1. Name the physical quantity, which changes the shape of a ball.

Ans. Force

2. Define the term force.

Ans. A force is a physical quantity which causes or tends to cause a motion in an object at rest or changes or tends to change the direction of motion of a moving object or the shape or size of the object.

3. Define balanced forces.

Ans. Two equal and opposite forces acting simultaneously on an object are known as balanced forces.

4. Define unbalanced forces.

Ans. Two forces of unequal magnitudes and acting in opposite directions on an object simultaneously are known as unbalanced forces.

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

Ans. Balanced forces are acting on the ball.

6. State Newton's first law of motion.

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

7. What do you mean by inertia ?

Ans. The tendency of a body to oppose any change in its state of rest or uniform motion is called inertia of the body.

8. On what factor does inertia of a body depend

Ans. Inertia of a body is directly proportional to its mass.

9. State S.I. unit of inertia.

Ans. S.I. unit of inertia is kilogram (kg.)

10. Which has more inertia : a man or a child ?

Ans. A man has more inertia than a child.

11. Which has more inertia : a twenty five paisa coin or a one rupee coin ?

Ans. A one rupee coin has more inertia than a twenty five paisa coin.

12. Which has more inertia : a train or a car ?

Ans. A train has more inertia than a car.

13. State Newton's second law of motion.

Ans. The rate of change of momentum of a body is directly proportional to the unbalanced force acting on it and the change in momentum takes place in the direction of the unbalanced force.

14. Force = mass x .............

Ans. Acceleration.

15. Define unit force.

Ans. A force is said to be unit force if it produces unit acceleration in body of unit mass.

16. Name the unit of force in SI.

Ans. newton (N).

17. Name the unit of force in CGS system.

Ans. dyne.

18. The rate of change of momentum of a particle is 5 kg ms². How much force acts on this body ?

Ans. F = rate of change of momentum = 5 N.

19. 1 newton = ......... dyne.

Ans. 10⁵.

20. Define 1 newton force.

Ans. Force is said to be newton if it produces 1 ms² acceleration in a body of 1 kg.

21. What is the relationship between force and acceleration ?

Ans. F = ma, where m is the mass of a body.

22. What is the name given to the product of man and acceleration of a body ?

Ans. Force (Q F = ma)

23. State Newton's third law of motion.

Ans. To every action, there is equal and opposite reaction.

24. Are action and reaction forces exist in pairs ?

Ans. Yes.

25. Are action and reaction forces act on same body or different bodies ?

Ans. Action and reaction act on the different bodies.

26. State whether the following statement is true or false. If false, correct it.

"Action and reaction are equal in magnitude and act in the same direction."

Ans. Action and reaction are equal in magnitude but opposite in directions.

27. State law of conservation of momentum.

Ans. The total momentum of a system remains constant if no external force acts on the system.

28. How much force acts on a body whose momentum is constant (i.e. = constant) ?

Ans. F = dp/dt. If p = constant, then no force acts on the body.

29. A fast moving truck loses momentum equal to 2 kg ms¹ after colliding with a stationary car. Will the car lose or gain momentum ? How much momentum is lost or gained by the car if the truck comes to the rest after collision ?

Ans. The car will gain momentum. Momentum gained by the car = 2 kg ms¹.

30. What do you mean by recoil velocity of a gun ?

Ans. The velocity with which a gun moves backward after firing a bullet is called the recoil of the gun.

Numerical Questions :

1. A constant force acts on an object of mass 5 kg for a duration of 2 s. It increases the object's velocity from
3 m s^_1 to 7 m s^_1. Find the magnitude of the applied force. Now if the force was applied for a duration of 5 s, what would be the final velocity of the object?

2. Which would require a greater force - accelerating a 2 kg mass at 5 m s^_2 or a 4 kg mass at 2 m s^_2?

3. A motorcar is moving with a velocity of 108 km/h and it takes 4 s to stop after the brakes are applied. Calculate the force exerted by the brakes on the motorcar if its mass along with the passengers is 1000 kg.

4. A force of 5 N gives a mass m₁, an acceleration of 10m s^_2 and a mass m₂, an acceleration of 20 m s^_2. What acceleration would it give if both the masses were tied together?

5. The velocity-time graph of a ball of mass 20 g moving along a straight line on a long table is given in figure.
How much force does the table exert on the ball to bring it to rest?

6. A bullet of mass 20g is horizontally fired with a velocity 150 ms^_1 from a pistol of mass 2 kg. What is the recoil velocity of the pistol ?

7. A girl of mass 40 kg jumps with a horizontal velocity of 5 ms^_1 onto a stationary cart with frictionless wheels. The mass of the cart is 3kg. What is her velocity as the cart starts moving ? Assume that there is no external unbalanced force working in the horizontal direction.

8. Two hockey players of opposite teams, while trying to hit a hockey ball on the ground collide and immediately become entangled. One has a mass of 60 kg and was moving with a velocity 5.0 m s^_1 while the other has a mass of 55 kg and was moving faster with a velocity 6.0 m s^_1 towards the first player. In which direction and with what velocity will they move after they become entangled? Assume that the frictional force acting between the feet of the two players and ground is negligible.

9. A body of mass 300 gm is at rest. What force in Newton will you have to apply to move it through 200 cm in 10 sec.?

10. A boat of mass 3000 kg, initially at rest is pulled by a force of 1.8 × 10⁴ Newton through a distance of 3 m. Assuming that the resistance due to water is negligible, What is the velocity of boat ?

11. A 40 kg slab rests on a frictionless floor. A 10 kg block rests on top of the slab. The static coefficient of friction between the block and the slab is 0.60 while the kinetic coefficient is 0.40. The 10 kg block is acted upon by horizontal force 100 N. If g = 9.8 m/s², then what resulting acceleration of the slab will be.

12. A body of mass 500 g is at rest on a frictionless surface. Calculate the distance travelled by it in 10s when acted upon by a force of 10² N.

13. A bullet of mass 5 g travelling at a speed of 120 ms¹ penetrates deeply into a fixed target and is brought to rest in 0.01s. Calculate : (a) the distance of penetration in the target, (b) the average force exerted on the bullet.

14. How much momentum will a dumbbell of mass 10 kg transfer to the floor, if it falls from a height of 0.8 m ? Take acceleration due to gravity as 10 ms².

15. A cricket ball of mass 70 g, moving with a velocity of 0.5 ms¹ is stopped by a player in 0.5s. What is the force applied by the plater to stop the ball?

Long answer type questions :-

1. State and prove the law of conservation of moemntum.

2. State the three laws. of Newton. Explain how the I law is seen in II law. Write the significance of a I and II laws.

3. Define inertia. Does it depend on the mass of the body ? How will you use this inertia to

(i) dust a carpet (ii) remove water drops from wet cloth ? Explain.

4. State the law of conservation of momentum. Explain how this law reasons.

(i) recoil of a gun (ii) motion of a rocket.

5. State Newton's three laws of motion. Find a mathematical expression for it.

6. If a coin is placed on a piece of cardboard resting on top of a jar, it is possible to fllick the card away sharply so that the coin falls into the jar. Explain why this is so ?

7. A person standing on a bus is thrown towards the rear of the bus as it begins to move and to the front of it as it slows down. Why?

8. Since action and reaction forces are always equal and opposite, how can motion then take place ?

9. Derive the relationship F = , where each symbol has its usual significance.

10. How can you explain flying of an aeroplane in terms of Newton's laws of motion ?

11. Why a person is likely to get more hurt when he falls on concrete floor than on loose mud or sand ?

12. What is the law of inertia ? Name the scientist who first stated this law. Describe a simple experiment to demonstrate the inertia of rest.

13. When a carpet is beaten with a stick, dust comes out of it. Explain.

14. Why it is advised to tie any luggage kept on the roof of a bus with a rope?

15. Explain with example Newton's First, Second and Third Law's of motion.

Formative assessment

Latest research based questions :

1. Failure of Newton's law when bodies move with a velocity comparable to the velocity of light.

2. Different fuels for propulsion of a rocket.

Topics of group discussion / (internet search) :

1. Discussion on balanced and unbalanced forces.

2. Newton's third law of motion and its applications in daily life.

3. Conservation of momentum : a universal phenomenon.

Activity based questions :

1. Describe an activity of demonstrates the property of inertia of rest of an object.

2. Describe an activity to show that action and reaction are equal and opposite.

3. Describe an activity to demonstrate the law of conservation of linear momentum.

ANSWER KEY

1. v = 13 m/s

2. accelerating a 2kg mass at 5ms^_2 would require a greater force.

3. - 7500 N

4. 6.67 m/s²

5.  - 0.0004 Newton

6. v = - 1.5 m/s

7. 4.65 m/s

8.  - 0.26 m/s

9. 0.012 N

10. 6 m/s

11. 0.98 m/s²

12. 1m

13. (a) 0.6m, (b) 60 N

14. 40 Ns

15. 0.07 N