9P02_Force and Laws of Motion_Avanti Module

9P02 – Force and Laws of Motion 19 Fifth Edition 9P02. Force and Laws of Motion TABLE OF CONTENTS 9P02. Force and Laws of Motion 19 9P02.1 Introduction to Force and Friction ……………………………………………………………………………………..……20 9P02.2 Inertia and Newton’s First Law of Motion …………………………………………………………………………………..22 9P02.3 Momentum and Newton’s second law of motion ………………………………………………………………….……24 9P02.4 Conservation of momentum and Newton’s third law of motion ………………………………………………….27 CBSE Practice Problems …………………….……….........………….………………….………………….………………………………..30 Olympiad Practice Problems …………………….……….........………….………………….…………...………………………………..32

9P02 – Force and Laws of Motion 20 D) Zero 9P02.1 Introduction to Force and Friction CONCEPTS COVERED 1. Definition of force 2. Affects of force on matter 3. Representation of forces 4. Balanced and unbalanced 5. Definition of friction 6. Affects of friction on motion IN CLASS EXERCISE Q1. What is a force? What is its SI unit? Q2. State the various effects produced by a force acting on an object. Q3. Given below is the distance-time table of an object in motion: Time in seconds Distance in metres 0 0 1 1 2 8 3 27 4 64 5 6 125 7 216 343 What conclusion can you draw about its acceleration? Is it A) Constant B) Increasing C) Decreasing Q4. When are forces said to be balanced? Q5. If ������ and ������′ are balanced forces, what will be the magnitude of ������2? Q6. What is friction? Q7. Friction between any two objects is due to B) Repulsion between them D) Irregularities on the surfaces A) Attraction between them C) Some adhesive forces between them Q8. How can you reduce friction between two objects? Q9. While riding a bicycle, if we stop pedaling, why does the bicycle slow down? Q10. Why is fuel required to run a car on a straight path if it is moving in a straight line on a horizontal surface with constant speed? 9P02.1

9P02 – Force and Laws of Motion 21 HOMEWORK Q1. Give an example to show that force can I. Make an object start moving from rest II. Make an object come to rest from motion III. Change the shape of an object Q2. What are unbalanced forces? Give examples. Q3. Are the forces acting on the following objects balanced? I. II. Q4. How does frictional force affect an object? Q5. What do you mean by ‘contact force’? Give an example. Q6. A ball moving on a table top eventually comes to rest. Explain the reason. Q7. Why do we sprinkle talcum powder on a carom board? ADVANCED QUESTIONS Q1. Does the application of force always require physical contact between two objects? Think about at least three real life examples where there is no physical contact between objects where forces are acting. Also try and identify causes of these forces. Q2. Is it possible for a particle to describe a curved path if no force acts on it? 9P02.1

9P02 – Force and Laws of Motion 22 9P02.2 Inertia and Newton’s First Law of Motion CONCEPTS COVERED 1. Defining the laws of motion 2. Inertia 3. Measurement of Inertia 4. Defining state of motion 5. Newton’s first law of motion and its applications IN CLASS EXERCISE Q1. Define inertia. What are the different types of inertia? Give examples. Q2. How is inertia of an object measured? Q3. What is Newton’s first law of motion? Q4. The inertia of a moving object depends on B) Speed of the object A) Colour of the object D) Shape of the object C) Mass of the object Q5. A father has mass 60kg and the mass of his son is 30kg. The ratio of inertia of father to his child is A) 1: 1 B) 1: 2 C) 2: 1 D) 1: 3 Q6. An automobile travelling with a speed of 60 ������������/ℎ, can stop within a distance of 20 ������ by applying brakes. If it is travelling twice as fast, i.e. 120 ������������/ℎ, the stopping distance will be A) 20 ������ B) 40 ������ C) 60 ������ D) 80 ������ Q7. An athlete always runs some distance before taking a jump. Why? Q8. There are three solids made up of aluminium, steel and wood of the same shape and volume. Which of them would have maximum inertia? Q9. What is the need for having seat belts in cars? Q10. Why does Newton’s first law of motion appear to be contradicted in our day-to-day life? HOMEWORK Q1. What is the relationship between inertia and mass of an object? Q2. Why do we jerk wet clothes before spreading them on string? Q3. A bullet fired against a glass pane makes a hole in it and the glass pane is not cracked. But on the other hand, when a stone is thrown at the same glass pane, it gets smashed. Why does this happen? Q4. Why is it easier to push an empty box compared to a box full of books? Q5. Why does a bowler take a run up while bowling at a cricket match? Q6. Why is it advised to tie luggage kept on the roof while travelling in a bus? Q7. Why does a rider on a horse fall back when the horse starts running all of a sudden? 9P02.2

9P02 – Force and Laws of Motion 23 ADVANCED QUESTIONS Q1. An object moves on a horizontal friction-less table with a constant velocity ������. Which of the following graphs best describes the acceleration of the particle as a function of time when no force is acting on it? A) acceleration B) acceleration 0 time 0 time C) D)acceleration acceleration 0 time 0 time Q2. A stuntman wants to jump from a moving bus for a stunt. In which direction should he jump to avoid injury as much as possible? A) In the direction of motion of the bus B) In the direction opposite to that of the bus C) Perpendicular to the direction of motion of the bus. Q3. In which of the following cases will an object experience zero net force? A) An object moving in a straight line with uniform speed. B) An object moving in a straight line with increasing speed. C) An object moving in a circular path with uniform speed. D) An object moving in a straight line with decreasing speed. Q4. Four cars are moving in a parking lot with different motions. Inside which of the following cars will the Newton's first law of motion hold true? A) A car moving in a straight line slowing down. B) A car moving in a circular path at constant speed. C) A car moving in a straight line at a constant speed D) A car moving in a straight line speeding up. Q5. There is a pile of similar carom coins on a table. Then, using a striker, the bottom most coin of the pile is removed so that the other coins are not disturbed. I. What will happen if the hit is strong enough? II. What will happen to the remaining coins once the bottom most coin is removed? 9P02.2

9P02 – Force and Laws of Motion 24 9P02.3 Momentum and Newton’s second law of motion CONCEPTS COVERED 1. Definition of momentum 2. Cause of change in momentum 3. Force-momentum relation 4. Newton’s second law of motion IN CLASS EXERCISE Q1. What is momentum? Define it mathematically. Q2. What is the SI unit of momentum? Is it a vector quantity? Q3. State Newton’s second law of motion. What is its mathematical application? Q4. How can Newton’s first law of motion be obtained from the second law of motion? Q5. Why does a small mass such as a bullet kill a person when fired from a gun? Q6. A rain drop of mass 0.1 ������ is falling with uniform speed of 10 ������������/������. What is the net force acting on the drop? A) Zero B) 10−3������ C) 2 × 10−2������ D) 10−2������ Q7. Two similar vehicles are moving with the same velocity on the road such that one of them is loaded and the other one is empty. Which of the vehicles will require larger force to stop it? Give reasons. Q8. Why a person is hurt less when he falls on a soft surface? Q9. A cricket ball of mass 70 ������ moving with a velocity of 0.5 ������/������ is stopped by a player in 0.5 ������. What is the force exerted by the player to stop it? Q10. A force of 30 ������ produces acceleration of 2 ������/������2 in a body of mass ������. Find the mass of the body. Also, find the acceleration if the force is doubled in magnitude along the same direction. Q11. Find the acceleration and force acting on a body of mass 4 kg using the following ������-������ graph. Q12. A man throws a ball weighing 500 ������ vertically upwards with a speed of 20 ������/������. I. What will be its initial momentum? II. What would be its momentum at the highest point of its flight? 9P02.͵

9P02 – Force and Laws of Motion 25 HOMEWORK Q1. State Newton’s second law of motion. What information do you get from it? Q2. How does Newton’s second law of motion differ from first law of motion? Q3. What is momentum? Write its SI unit. Interpret force in terms of momentum. Q4. Name the S.I. unit of force and define it mathematically. Q5. Glass utensils are wrapped in hay during their transportation. Justify giving reason. Q6. By how much does the momentum of a body of mass 5 ������������ change when its speed I. Decreases from 20 ������/������ to 0.20 ������/������; and II. Increases from 30 ������/������ to 40 ������/������? Q7. A force of 5 ������ produces an acceleration of 8 ������/������2 on a mass ������1 and an acceleration of 24 ������/������2 on mass ������2. What acceleration would the same provide if both the masses are tied together? Q8. The speed-time graph of a car of 1000 ������������ mass is given. On the basis of this, answer the following questions. I. When is the maximum force acting on car? II. What is the retarding force acting on the car? III. For how long is the force not acting on the car? IV. Find the acceleration of the car during each of the first four seconds and fourth to eighth second. Q9. If the engine of a car provides an acceleration of 2 ������/������2 to start it from rest, assuming the mass to be roughly 1000 ������������, calculate: I. Force provided by the engine. II. Momentum after 10 ������. Q10. The velocity – time graph of a ball of mass 30g moving along a straight line on a long table is given in the figure below. How much force does the table exert on the ball to bring it to rest? 9P02.͵

9P02 – Force and Laws of Motion 26 Q11. A bullet of mass 4 ������ when fired with a velocity of 50 ������/������, can enter a wall up to a depth of 10 ������������. How much will be the average resistance offered by the wall? ADVANCED QUESTIONS Q1. How do karate experts break huge blocks of bricks with their bare hands? Q2. A block of mass 2kg placed on a long frictionless table is pulled horizontally by a constant force F. It is found to move 10m in the first two seconds. Find the magnitude of F. Q3. A car moving at 40 km/hr is to be stopped by applying brakes in the next 4 m. If the car weighs 2000 kg, what average force must be applied on it? Q4. Force of 10N applied to a mass ������1 produces an acceleration of 5 ������/������2 and when applied to mass ������2, produces an acceleration of 15 ������/������2 in the mass. How much acceleration will the same force produce if the two masses are tied together? 9P02.͵

9P02 – Force and Laws of Motion 27 9P02.4 Conservation of momentum and Newton’s third law of motion CONCEPTS COVERED 1. Action and reaction forces 2. Newton’s third law of motion 3. Definition of normal force 4. Conservation of momentum in an ideal isolated system IN CLASS EXERCISE Q1. State Newton’s third law of motion. Q2. What are action and reaction forces? Give examples Q3. State the action and reaction forces in the following cases: II. Hammering a nail IV. A moving rocket I. Firing a bullet from a gun VI. A moving train colliding with a stationary III. A book lying on a table V. A person walking on the floor train Q4. Why does a boat tend to leave the shore, when passengers are getting off from it? Q5. Explain the working of a rocket. Q6. A boy pushes a wall with a force of 10 N towards east. What force is exerted by the wall on the boy? Q7. Does Newton’s third law of motion apply to a system where bodies do not actually touch each other? Q8. What do you mean by conservation of momentum? Q9. A heavy car ������ of mass 2000 ������������ travelling at 30 ������/������ has a head-on collision with a sports car ������ of mass 1000 ������������. If both cars stopped on colliding, what was the velocity of car ������? Q10. A bullet of mass 20 ������ is horizontally fired with a horizontal velocity 150 ������/������ form a pistol of mass 2 ������������. What is the recoil velocity of the pistol? Q11. Solve the crossword with the help of hints given below: Across 2. The speed of an object in a given direction 4. A push or pull than can also change the shape of an object 5. The measure of the force of gravity on an object 8. When objects are in motion and hit each other 9. The SI unit of force 10. Mass of object times its velocity 11. Tendency of an object to remain in motion or rest Down 1. Shortest distance between final and initial position 3. Rate of change of velocity 6. A force that always acts opposite to direction of motion 7. The rate at which an object changes its position 9P02.Ͷ

9P02 – Force and Laws of Motion 28 HOMEWORK Q1. State the law of action and reaction forces. Q2. Why are road accidents at high speeds worse than accidents at low speeds? Q3. Why are buffers provided between the bogies of a railway train? Q4. If a balloon is filled with air and its mouth untied, air is released from its mouth in the downward direction. Write the other observations made by you. Justify your answer. Q5. A truck of mass ������ is moved under a force ������. 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 an acceleration change? Q6. State the law of conservation of momentum. Prove this law by taking the case of collision of two bodies. Q7. The motion of a body of mass 5 ������������ is shown in the ������ − ������ graph. Find from the graph: I. Its acceleration, II. The force acting on the body, and III. The change in momentum of the body 2 seconds after start. Q8. Since action and reaction forces are always equal in magnitude and opposite in direction, how can anything ever be accelerated? Q9. A horse cannot pull a cart and run in space. Why? 9P02.Ͷ

9P02 – Force and Laws of Motion 29 Q10. A bullet of mass 20 ������ moving with a speed of 500 ������/������ strikes a wooden block of mass 1������������ and gets embedded in it. Find the speed with which block moves along with the bullet. Q11. A body of mass 2 ������������, initially moving with a velocity of 10 ������/������ collides with another body of mass 5 ������������ at rest. After collision velocity of first body becomes 1 ������/������. Find the velocity of the second body. ADVANCED QUESTIONS Q1. Can the normal force acting on one body in contact with another body ever be a pulling force instead of a pushing force? A) Yes B) No C) Depends on the nature and material of the surfaces in contact D) Depends on the shape of surfaces in contact Q2. According to Newton’s third law each team pulls the opposite team with equal force in a tug of war. Why is it then that does one team wins and the other loses? Q3. A car accelerates on a horizontal road due to the force exerted by A) The engine of the car B) The driver of the car C) The earth D) The road 9P02.Ͷ

30 Avanti 9P02 Force and Laws of Motion CBSE Practice Problems

31 Avanti 9P02 Force and Laws of Motion CBSE Practice Problems

32 9P02 – Force and Laws of Motion – Olympiad Practice Problems INSTRUCTIONS Answer each of the following questions. 1. DIRECTION: Study the diagram given below and answer question 1 and 2 (The diagrams are not drawn to scale). What is the extension of spring in figure (iii)? A) 6 B) 9 C) 12 D) 15 2. Springs and are similar. What is the length of spring in figure (iv)? A) 6 B) 9 C) 12 D) 15 3. The sliding frictional force between 4 box and the floor is 15 . It is pushed across the floor with a constant force such that it accelerates at 0.8 . What is the force applied to the box? A) 16.6 B) 18.2 C) 20 D) Zero 4. A 500 rocket sled can be accelerated at a constant rate from rest of 1600 in 1.8 . What is the magnitude of the required net force? A) 1.2 × 10 B) 1.2 × 10 C) 2.4 × 10 D) 2.4 × 10 5. A jet plane starts from rest on the runway and accelerates for takeoff at 2.30 . It has two jet engines, each of which exerts a thrust of 1.40 × 10 . What is the weight of the plane? A) 1.19 × 10 B) 2.80 × 10 C) 2.38 × 10 D) 4.17 × 10 6. A person used force , shown in figure to move a load with constant velocity on a surface. Identify the correct surface profile. A) B) C) D) Avanti – 9P02 – Force and Laws of Motion – Olympiad Practice Problems

7. A cricket ball of mass 150 moving with a speed of 126 / hits at the middle of the bat, held firmly at its position 33 by the batsman. The ball moves straight back to the bowler after hitting the bat. Assuming that collision between ball and bat is completely elastic and the two remain in contact for 0.001 , the force that be batsman had to apply to hold the bat firmly at its place would be _________. A) 10.5 B) 21 C) 1.05 × 10 D) 2.1 × 10 8. A body of mass moving with a uniform velocity collides with another body of mass at rest and then the two together begin to move with a velocity .The ratio of [3 ( + )] to [4 ] is A) 9 1 B) 12 1 C) 16 1 D) Data insufficient 9. Two identical satellites and resolve round the earth in circular orbits at distance and 3 respectively from the surface of the earth, where is the radius of the earth. The ratio of linear momenta of to is A) 3 1 B) 1 3 C) 2 1 D) 1 2 10. An object of mass travelling to the right with velocity 2 collides with another object of mass 2 travelling to the left with velocity 3 as shown in the figure. After the collision, the objects stick together. Which of the following options is correct regarding the total momentum (magnitude) and total kinetic energy of the two objects? Momentum Kinetic energy A. 0 0 B. 6 C. 4 (1/2) D. 4 (8/3) (4/3) 11. Read the given statements and select the correct option. Statement 1: If a body is thrown vertically upward from ground and air resistance is taken in account, then the time of ascent is less than the time of descent. Statement 2: Air resistance opposes the motion of the body. A) Both statement 1 and statement 2 are true and statement 2 is the correct explanation of statement 1. B) Both statement 1 and statement 2 are true but statement 2 is not the correct explanation of statement 1. C) Statement 1 is true but statement 2 is false. D) Statement 1 is false but statement 2 is true. 12. Which of the following statement(s) is /are correct? (i) A car accelerates on a horizontal straight road due to the force exerted by the road. (ii) All conservation laws such as conservation of momentum, energy, charge etc are considered to be a fundamental laws in physics. (iii) A passenger in a decelerating train on a straight track tosses a coin which falls behind him. A) (i) Only B) (ii) and (iii) only C) (i) and (ii) only D) (i), (ii) and (iii) 13. A body of mass is accelerated by a constant force. Which graph best shows the variation of momentum ( ) of the body with the displacement(s). The body starts from rest? 14. A block of mass is supported by a cord from a rigid support and another cord is attached to the bottom of the block as shown in the figure. Which of the following statement is correct? A) If you give a sudden jerk to , it will break. B) If you give a sudden jerk to , will break. C) If you pull on steadily, chord will break. D) Both options and are correct. Avanti – 9P02 – Force and Laws of Motion – Olympiad Practice Problems

15. The figure shows two horizontal forces acting on a block on a frictionless floor. If third horizontal force also acts on 34 the block, what are the magnitude and direction of when the block is moving to the left with a constant speed of 5 /? A) 2 leftward B) 2 rightward C) 8 leftward D) 8 rightward 16. A small block of mass 1 is placed on block of mass 5 and length 20 as shown in figure. A constant horizontal force of 10 is applied on block if all the sur- face are assumed frictionless and block is at the right end of block , then the time in which block separates from is A) 0.2 B) 0.5 C) 2 D) 3 17. Read the given statements and select the connect option. Statement-1: A cloth covers a table. Some dishes are kept on it. The cloth can be pulled out without dislodging the dishes from the table. Statement-2: For every action. There is an equal and opposite reaction. A) Both statements-1 and 2 are true and statement-2 is the correct explanation of statement-1. B) Both statements-1 and 2 are true but statement-2 is not the correct explanation of statement-1 C) Statement-1 is true and statement-2 is flase. D) Both statements-1and 2 are false. 18. A block accelerates sown a slope, as shown in the figure. The upper portion of the slope is smooth and lower portion is rough. On the lower portion, (i) The speed of the block may increase, decrease or remain same. (ii) The acceleration of block reduces. (iii) The mass of block reduces. Which of the following is/are correct? A) (i) only B) (i) and (ii) only C) (ii) and (iii) only D) (i), (ii) and (iii) 19. Read the given statements and select the correct option. Statement 1: The value of dynamic friction is less than the limiting friction. Statement 2: Once the motion has stared, the inertia of rest has been overcome. A) Both statements 1 and 2 are true and statement 2 is the correct explanation of statement 1. B) Both statements 1 and 2 are true but statement 2 is not the correct explanation of statement 1. C) Statement 1 is true and statement 2 is false. D) Both statements 1 and 2 are false. 20. A scooterist moving with a speed of 36 sees a child standing in the middle of the road. He applies the brakes and brings the scooter to rest in 5 just in time to save child. If mass of the scooter and driver is 300 , the average retarding force on the scooter is A) 6 × 10 B) 6 × 10 C) 6 × 10 D) 6 × 10 21. Read the given statements and select the correct option. Statement 1: Force of friction between two surfaces depends on the area of contact common to the two surfaces. Statement 2: more the area of contact common to the two surfaces, more is the opposition to the motion. A) Both statements 1 and 2 are true and statement 2 is the correct explanation of statement 1. B) Both statement 1 and 2 are true but statement 2 is not the correct explanation of statement 2. C) Statement 1 is true but statement 2 is false. D) Both statements 1 and 2 are false. Avanti – 9P02 – Force and Laws of Motion – Olympiad Practice Problems

22. Two spheres of the same size but different masses make head-on collisions. The black sphere is half the mass of the 35 white sphere. In each collision, one of the masses is initially at rest and both masses move after the collision. Which of the situations shows a possible collision? 23. Read the given statements and select the correct option. Statement 1: The forces of action and reaction always appear due to actual physical contact of two bodies. Statement 2: A particle can move only under the action of a force. A) Both statements 1 and 2 are true and statement 2 is the correct explanation of statement 1. B) Both statement 1 and 2 are true but statement 2 is not the correct explanation of statement 1. C) Statement 1 is true but statement 2 is false. D) Both statements 1 and 2 are false. 24. A bicycle is being pedaled on a horizontal road. The forces of friction between the road and the front and rear wheels are and respectively. Then A) Both and act in the forward direction. B) Both and act in the backward direction. C) acts in the forward direction, acts in the backward direction. D) acts in the backward direction, acts in the forward direction. 25. A ball of mass 400 is dropped from a height of 5 . A boy on the ground hits the ball vertically upwards with a bat with an average force of 100 , so that it attains a vertical height of 20 . The time for which the ball remains in con- tact with the bat is (Take = 10 ) A) 0.08 B) 0.12 C) 2 D) 5 26. A particle of mass 70 , moving at 50 , is acted upon by a variable force opposite to its direction of motion. The force is shown as a function of time. After the force stops acting, the particle moves with a speed of A) 50 in reverse direction B) 100 in reverse direction D) 100 in original direction C) 150 in original direction Avanti – 9P02 – Force and Laws of Motion – Olympiad Practice Problems