FORCE AND LAW OF MOTION 9

Practice Paper
Subject Physics (2020)

                               CH- 9 FORCE AND LAW OF MOTION                           

CLASS IX

I. Very Short answer type questions: 

1. What is the approximate value of g?
2. Name the scientist who proved for the first time that objects move with constant speed when no force acts on them.
3. When a body is said to be in equilibrium?
4. Define the resultant force.
5. What is the S.I unit of force?
6. Is momentum a scalar or a vector quantity?
7. Write the expressions of force and weight.
8. In a tug of war, the rope does not move in any direction. Why?
9. Define 1-Newton force.
10. Define linear momentum.
11. Write the expression and unit of momentum.
12. Name the force which is responsible for the change in position or state of an object.
13. Define Inertia.
14. What is the relation between inertia and mass?
15. Which has the highest inertia solid made of aluminium, steel, and wood of the same shape and volume?
16. Name the unbalanced force which slows down a moving bicycle when we stop paddling it.
17. Give one point of difference between a balanced and unbalanced force.
18. Why does the sole of the shoe wear?
19. A force is applied on a metal block lying on the floor in one direction. Still, the block does not move. Name the force which is balancing it.
20. Find the acceleration produced by a force of 12 N exerted on an object of mass 3 kg.
21. Find the momentum of a man of mass 75 kg when he walks with a velocity of 2 m/s. 
22. The mass of a body is doubled. How does its acceleration change under a given force?
23. Write any two kinds of changes or effects a force can produce in a nonrigid body fixed at a position.
24. When a carpet is beaten with a stick it releases dust. Explain why?
25. State an example, how force can change the velocity of a body?
26. Why are the athletes in a high jump even made to fall either on a cushioned bed or on a sand bed?
27. A ball is thrown vertically upwards. What is its momentum at the highest point?
28. Name the physical quantity which is measured by the rate of change of momentum.
29. What is the physical quantity of inertia and its S.I unit?
30. During the game of table tennis, if the ball hits a player it does not hurt him. On the other hand, when a fast-moving cricket ball hits a spectator it may hurt him. State the reason.
31. If the initial velocity is zero then the force acting is:-
    (a) Retarding (b) Acceleration (c) Both (d) None.
32. A force is applied on a metal block lying on the floor in one direction. Still, the block does not move. Name the force which is balancing it.
33. Name the physical principle on which jet aircraft work.

II. Short answer type questions:

1. When we can say that the balanced or unbalanced force acts on an object?
2. Define Balanced and unbalanced force.
3. Define force and write the types of force? 
4. On what factors does the momentum of a body depend?
5. What is the magnitude and direction of resultant force if two forces of magnitude F each act at a point toward the right?
6. Define the conservation of linear momentum.
7. Why does a person in a bus tend to fall forward, when it stops suddenly?
8. Give an example where two equal and opposite forces do not form an action-reaction pair.
9. State Newton's first law. Why is it known as the law of inertia?
10. Differentiate between mass and weight?
11. What are the factors on which inertia depends?
12. State Newton's second law of motion.
13. State Newton's second law in terms of momentum.
14. Explain Newton's first law in terms of the second law. 
15. A book kept on a table. There are two forces on the book -normal force in an upward direction and gravitational force in a downward direction. Is this pair of force is an action-reaction pair? Explain your answer.
16. Define inertia. What are the two types of inertia?
17. If an object experiences a non zero external unbalanced force. Is it possible for the object to be traveling with a non zero velocity? State your answer.
18. A karate player can break a pile of tiles in a single blow with his hands. How?
19. Raju is having three solid blocks of the same size and shape and made up of steel, wood, and plastic. Which one of these will have the highest inertia? Give the reason for your choice.

III. Long answer type questions: 

1. Define (i) force (ii) Contact force (iii) Non contact force (iv) Frictional force.
2. When a wheel rolls on the level ground, what is the direction of frictional force at the point of contact of the wheel and ground? How is it in accordance with Newton's third law of motion?
3. When a tree is shaken, its fruits and leaves fall down. Why?
4. Mention the action and reaction forces for a man walking on the road.
5. Action and reaction forces act on the same or different bodies? Explain and justify your answer.
6. Using the second law of motion derives the relation between force and acceleration.
7. When a carpet is bitten with a stick it releases dust. Explain why?
8. State an example, how force can change the velocity of a body?
   Write the type of force acting between moving body and floor.
9. (a)If action is always equal to the reaction, explain how a horse can pull a cart?
   (b) Write the units of force and momentum.
10. Interpret force in terms of momentum. Represent the following graphically. (i) Momentum versus velocity when mass is fixed (ii) Momentum versus mass when velocity is constant.
11. (a) To start walking we push the ground in the backward direction. Why?
    (b) Why the athletes are in a high jump event made to fall on the sand or cushioned bed?
12. If the table tennis ball hits a player it does not hurt him but a fast-moving ball may hurt him. Why?
13. Water sprinkled used for the grass lawn being to rotate as soon as the water is supplied. Explain the principle on which it works
14. By applying force, if the object does not move then what type of force is acting on it?  
15. State Newton’s third law of motion and how does it explain the walking of man on the ground.
16. When a bullet is fired from a gun, the gun recoils. Why? 
17. Two identical bullets are fired, one by a lighter rifle and another by a heavy rifle with the same force. Which rifle will hurt the shoulder more and why? 
18. When a cricketer fielding near the boundary takes a high catch, he moves his hands downward with the ball. Why does he do that?
19. Explain why is it difficult for a Fireman to hold a hose which ejects a large amount of water at a high velocity.
20. (a) A horse is continuous to apply a force in order to move a cart with a constant velocity. Explain why? 
    (b) 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?
21. Prove the principle of conservation of linear momentum for two bodies moving in the same direction and coiling.
22. A ball of mass m is thrown vertically upward with an initial velocity V. Its speed decreases continuously till it becomes zero. Thereafter, the ball begins to fall downward and attains the speed V again before striking the ground. It implies that the magnitude of the initial and final momentum of the ball is the same. Yet it is not an example of conservation of momentum. Explain why?
23. Write the factors on which solid and liquid pressure depends.

  Numerical:

1. What is the momentum of a body of mass 200g moving with a velocity of 15 m/s? 
2. A cheetah accelerates from rest at the rate of 4 m/s.
   (a) What will be the velocity attained by it in 10 s?
   (b) How far will it travel in this duration? 
3.  A force of 25 N acts on a mass of 500 g resting on a frictionless surface. What is the acceleration produced? 
4. A force of 15 N acts for 5 s on a body of mass 5K g which is initially at rest. Calculate :
   (a) the final velocity of the body b) the displacement of the body. 
5. A scooter is moving with a velocity of 20 m/s when brakes are applied. The mass of the scooter and the rider is 180 Kg. the constant force applied by the brakes is 500 N. 
   (a) How long should the brakes be applied to make the scooter comes to a halt?  
   (b) How far does the scooter travel before it comes to rest?
6. A stone is dropped from a 100 m high tower. How long does it take to fall?  
   (i) the first 50 m and (ii) the second 50 m.
7. From a rifle of mass 4 kg, A bullet of mass 50 grams is fired with an initial velocity of 35 m/s. Calculate the initial recoil velocity of the rifle. Two objects of mass 100 g and 200 g are moving along the same direction with a velocity of 2m p/s and 1 m p/s respectively. They collide and after the collision, the first object moves at a velocity of 1.67 m/s. Determine the velocity of the second object. 
8. 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. 
9. A bullet of mass 10 g strikes a sandbag at a speed of 10³ m/s and gets embedded after traveling 5 cm. Calculate
   (i) the resistive force exerted by the sand on the bullet
   (ii) the time is taken by the bullet to come to rest.
10. Derive the unit of force using the second law of motion a force of 5 Newton produce an acceleration of 8 m/s²on a mass M1 and an acceleration of  24 m/s on a mass M2. What acceleration of the same force provide if both the masses are tied together.
11. A force produces an acceleration of 0.5 m/s² in a body of mass 3.0 Kg. If the same force acts on a body of mass 1.5 kg, what will be its acceleration?
12. A force produces an acceleration of 5.0 m/s² when it acts on a body of mass 20 grams. Find the force in Newton.
13. A force acts on a particle of mass 200 gm. The velocity of the particle changes from 15 m/s to 25 m/s in 2.5 s. Assuming the force to be constant, find its magnitude.
14. A force produces an acceleration of 2.0  m/s² in a body and 5.0 m/s² in another body B. Find the ratio of the mass of A to the mass of B.
15. A force of 0.6 N on a particle increases its velocity from 5.0 m/s to 6.0 m per sec.in 2 sec. Find the mass of the particle.
16. A force acting on a particle of mass 200 gm displaces it through 400 cm in 2 sec. Find the magnitude of the force if the initial velocity of the particle is zero.
17. A bullet of mass 20 gm moving with a speed of 120 m/s strikes a thick muddy wall and penetrate into it. It takes 0.03 seconds to stop in the wall. Find:
    (a) the acceleration of the bullet in the wall,
    (b) the force exerted by the wall on the bullet,
    (c) the force exerted by the bullet on the wall, and d) the distance covered by the bullet in the wall.
18. A particle of mass 0.5 kg is kept at rest. A force of 2.0 N act on it for 5.0 sec. Find the distance moved by the particles in this 5.0 sec, and be the next 5.0 s.
19. A force of 1.0 N acts on a body of mass 10 kg. As a result, the body covers 100 cm in 4 sec, moving along a straight line. Find the initial velocity.
20. Which Newton’s law of Motion is applied in the flight of a bird? Support your answer with suitable reason.

NCERT QUESTIONS

1. Which of the following has more inertia: (a) a rubber ball and a stone of the same size? (b) a bicycle and a train? (c) a five rupee coin and a one-rupee coin? 
2. In the following example, try to identify the number of times the velocity of the ball changes: “A football player kicks a football to another player of his team who kicks the football towards the goal. The goalkeeper of the opposite team collects the football and kicks it towards a player of his own team”. Also, identify the agent supplying the force in each case. 
3. Explain why some of the leaves may get detached from a tree if we vigorously shake its branch. 
4. Why do you fall in the forward direction when a moving bus brakes to a stop and fall backward when it accelerates from rest?
5. If action is always equal to the reaction, explain how a horse can pull a cart.
6. Explain, why is it difficult for a fireman to hold a hose, which ejects large amounts of water at a high velocity.
7. From a rifle of mass 4 kg, a bullet of mass 50 g is fired with an initial velocity of 35 ms–1. Calculate the initial recoil velocity of the rifle.
8. 4. Two objects of masses 100 g and 200 g are moving along the same line and direction with velocities of 2 ms–1 and 1 ms–1, respectively They collide and after the collision, the first object moves at a velocity of 1.67 ms–1. Determine the velocity of the second object.
9. An object experiences a net zero external unbalanced force. Is it possible for the object to be traveling with a non-zero velocity? If yes, state the conditions that must be placed on the magnitude and direction of the velocity. If no, provide a reason.
10. When a carpet is beaten with a stick, dust comes out of it. Explain.
11. Why is it advised to tie any luggage kept on the roof of a bus with a rope?
12. A batsman hits a cricket ball which then rolls on level ground. After covering a short distance, the ball comes to rest. The ball slows to a stop because :
    (a) the batsman did not hit the ball hard enough. 
    (b) velocity is proportional to the force exerted on the ball. 
    (c) there is a force on the ball opposing the motion. 
    (d) there is no unbalanced force on the ball so the ball would want to come to rest.
13. A truck starts from rest and rolls down a hill with a constant acceleration. It travels a distance of 400 min 20 s. Find its acceleration. Find the force acting on it if its mass is 7 metric tonnes (Hint: 1 metric tonne = 1000 kg.) 
14. A stone of 1 kg is thrown with a velocity of 20 ms–1 across the frozen surface of a lake and comes to rest after traveling a distance of 50 m. What is the force of friction between the stone and the ice? 
15. An 8000 kg engine pulls a train of 5 wagons, each of 2000 kg, along a horizontal track. If the engine exerts a force of 40000 N and the track offers a friction force of 5000 N, then calculate: (a) the net accelerating force; (b) the acceleration of the train; and (c) the force of wagon 1 on wagon 2.
16. An automobile vehicle has a mass of 1500 kg. What must be the force between the vehicle and road if the vehicle is to be stopped with a negative acceleration of 1.7 ms–2?
17. What is the momentum of an object of mass m, moving with a velocity v? (a) (mv) 2 (b) mv2 (c) ½ mv2 (d) mv.
18. Using a horizontal force of 200 N, we intend to move a wooden cabinet across a floor at a constant velocity. What is the friction force that will be exerted on the cabinet?
19. Two objects, each of mass 1.5 kg, are moving in the same straight line but in opposite directions. The velocity of each object is 2.5 ms-1 before the collision during which they stick together. What will be the velocity of the combined object after the collision? 
20.  According to the third law of motion when we push on an object, the object pushes back on us with an equal and opposite force. If the object is a massive truck parked along the roadside, it will probably not move. A student justifies this by answering that the two opposite and equal forces cancel each other. Comment on this logic and explain why the truck does not move. 
21.  A hockey ball of mass 200 g traveling at 10 ms–1 is struck by a hockey stick so as to return it along its original path with a velocity at 5 ms–1. Calculate the change of momentum occurred in the motion of the hockey ball by the force applied by the hockey stick.
22. A bullet of mass 10 g traveling horizontally with a velocity of 150 ms–1 strikes a stationary wooden block and comes to rest in 0.03 s. Calculate the distance of penetration of the bullet into the block. Also, calculate the magnitude of the force exerted by the wooden block on the bullet.
23. An object of mass 1 kg traveling in a straight line with a velocity of 10 ms–1 collides with and sticks to, a stationary wooden block of mass 5 kg. Then they both move off together in the same straight line. Calculate the total momentum just before the impact and just after the impact. Also, calculate the velocity of the combined object.
24. An object of mass 100 kg is accelerated uniformly from a velocity of 5 ms–1 to 8 ms–1 in 6 s. Calculate the initial and final momentum of the object. Also, find the magnitude of the force exerted on the object.
25. Akhtar, Kiran, and Rahul were riding in a motorcar that was moving with a high velocity on an expressway when an insect hit the windshield and got stuck on the windscreen. Akhtar and Kiran started pondering over the situation. Kiran suggested that the insect suffered a greater change in momentum as compared to the change in momentum of the motorcar (because the change in the velocity of the insect was much more than that of the motorcar). Akhtar said that since the motorcar was moving with larger velocity, it exerted a larger force on the insect. And as a result, the insect died. Rahul while putting an entirely new explanation said that both the motorcar and the insect experienced the same force and a change in their momentum. Comment on these suggestions.
26. How much momentum will a dumb-bell of mass 10 kg transfer to the floor if it falls from a height of 80 cm? Take its downward acceleration to be 10 ms–2.
27. Two persons manage to push a motorcar of mass 1200 kg at a uniform velocity along a level road. The same motorcar can be pushed by three persons to produce an acceleration of 0.2 ms-2. With what force does each person push the motorcar? (Assume that all persons push the motorcar with the same muscular effort.) 
28. A hammer of mass 500 g, moving at 50 ms-1, strikes a nail. The nail stops the hammer in a very short time of 0.01 s. What is the force of the nail on the hammer?
29. A motorcar of mass 1200 kg is moving along a straight line with a uniform velocity of 90 km/h. Its velocity is slowed down to 18 km/h in 4 s by an unbalanced external force. Calculate the acceleration and change in momentum. Also, calculate the magnitude of the force required.
30. A large truck and a car, both moving with a velocity of magnitude v, have a head-on collision and both of them come to a halt after that. If the collision lasts for 1 s: 
    (a) Which vehicle experiences the greater force of impact? 
    (b) Which vehicle experiences a greater change in momentum?
    (c) Which vehicle experiences the greater acceleration? 
    (d) Why is the car likely to suffer more damage than the truck? 

CHAPTER 1 - MATTER IN OUR SURROUNDINGS	☛ QUESTION WITH SOLUTIONS
CHAPTER 2 - IS MATTER AROUND US PURE?	☛QUESTION WITH SOLUTIONS
CHAPTER 3 - ATOMS AND MOLECULES	☛ QUESTION WITH SOLUTIONS
CHAPTER 4 - STRUCTURE OF ATOM	☛   QUESTION WITH SOLUTIONS
CHAPTER 5 -  THE FUNDAMENTAL UNIT OF LIFE
CHAPTER 6 -  TISSUE
CHAPTER 7 -   DIVERSITY IN LIVING ORGANISM
CHAPTER 8 -  MOTION	☛ QUESTION WITH SOLUTIONS
CHAPTER 9 -  FORCE AND LAW OF MOTION	☛  QUESTION WITH SOLUTIONS
CHAPTER 10 - GRAVITATION	☛ QUESTION WITH SOLUTIONS
CHAPTER 11 -  WORK AND ENERGY
CHAPTER 12 -  SOUND
CHAPTER 13-  WHY DO WE FALL ILL
CHAPTER 14 - NATURAL RESOURCES
CHAPTER 15 - IMPROVEMENT OF FOOD RESOURCES