4.

LAWS OF MOTION
MULTIPLE CHOICE QUESTIONS:
1. No force is required to keep
(A) an object moving in circular motion
(B) an object moving in straight line with constant velocity
(C) an object moving with constant acceleration
(D) an object moving in elliptical path.
2. What is the term for an object’s tendency to resist changes in the state of motion?
(A) Friction (B) Force (C) Momentum (D) Inertia
3. The ratio of force on an object to its acceleration is:
(A) mass (B) velocity (C) momentum (D) mass density
4. What happens to the acceleration of an object when the force applied to it increases?
(A) Decreases (B) Remains constant (C) Increases (D) Become zero
5. When object A exerts a force on object B, what force does object B exert on object A?
(A) Equal force in same direction (B) Equal force in opposite direction
(C) Lesser force in same direction (D) Greater force in opposite direction
6. Forces always occurs in
(A) Triplets (B) Quarters (C) Pairs (D) None
7. Rocket works on the principle of conservation of:
(A) Energy (B) Momentum (C) Mass (D) All of these
8. A force F is applied to object for time Δt. What is the impulse?
(A) I = F/Δt (B) I = FΔt (C) I = ΔpΔt (D) I = Δp/Δt
9. The component of contact force that is perpendicular to the surface in contact is referred to as:
(A) Frictional force (B) Normal reaction force
(C) Both (A) and (B) (D) None of the mentioned
10. The spring force is given by
(A) F = kx (B) F = k/x (C) F = -k/x (D) F = – kx
11. A block of wood is placed on a surface. A force is applied parallel to the surface to move the
block. The frictional force developed acts
(A) along the direction of the applied force (B) opposite to the direction of applied force
(C) normal to the surface upward (D) normal to the surface downward
12. Which of the following is a self-adjusting force?
(A) Limiting friction (B) Dynamic friction (C) Sliding friction (D) Static friction.
13. Which of the following statement is correct?
(A) Friction does not depend on the area of contact
(B) Friction is always less than the applied force
(C) Friction depends on the size of the body
(D) Friction depends on the area of contact
14. On a banked road, which force is essential to provide the necessary centripetal force to a car to
take a turn while driving at the optimum speed?
(A) Component of frictional force
(B) Component of normal reaction
(C) Both (A) and (B)
(D) None of these
15. A cyclist bends while taking a turn in order to
(A) reduce apparent speed
(B) reduce friction
(C) reduce speed
(D) provide necessary centripetal force
16. Match the physical quantities of Column I with their dimensions in Column II.
Column I Column II
(i) Weight (a) [ ]
(ii) Acceleration (b) [ ]
(iii) Impulse (c) [ ]
(A) (i)-(a), (ii)-(c), (iii)-(b) (B) (i)-(a), (ii)-(b), (iii)-(c)
(C) (i)-(b), (ii)-(c), (iii)-(a) (D) (i)-(b), (ii)-(a), (iii)-(c)
17. Statement I: There is a stage when frictional force is not needed at all to provide the necessary
centripetal force on a banked road.
Statement II: On a banked road, due to its inclination the vehicle tends to remain inwards
without any chances of skidding.
(A) Both Statements I and Statement II are true and the Statement II is a correct explanation of the
Statement I.
(B) Both Statements I and Statement II are true but Statement II is not a correct explanation of the
Statement I.
(C) Statement I is true but the Statement II is false.
(D) Statement I and Statement II both are false.
18. Which one of the following statements is incorrect?
(A) Frictional force opposes the relative motion.
(B) Limiting value of static friction is directly proportional to normal reaction.
(C) Rolling friction is smaller than sliding friction
(D) Coefficient of sliding friction has dimensions of length.
19. A mass M kg is suspended from a spring balance, which in turn is hanging from the hook of
another spring balance. What will be the readings on both of these balances? (Neglect the mass
of the spring balances)
(A) Both will read M kg.
(B) Both will read M/2 kg.
(C) The lower one will read M kg, and the upper one zero.
(D) The sum of both their readings will be M kg.
20. Three blocks with masses m, 2m and 3m are connected by strings, as shown in the
figure. After an upward force F is applied on block m, the masses move upward at
constant speed v. What is the net force on the block of mass 2m? (g is the
acceleration due to gravity)
(A) 6 mg (B) Zero (C) 2 mg (D) 3 mg

21. A block slides down an inclined plane with angle θ. What is the force of kinetic
friction?
(A) = cos (B) = sin (C) = (D) = cos

FILL IN THE BLANKS:

(impulse, Nm-1, Nm, constant, zero, mass)
1. _________ is a measure of the inertia of a body.
2. When no external force is applied on a system, its total momentum is _____________
3. A force acting for a short duration is called _____________.
4. At equilibrium net force on a body is _________.
5. The SI unit of spring constant is __________.

TWO MARK QUESTIONS:

1. Name the two physical quantities which are defined on the basis of Newton's first law.
2. Write the expression for momentum in vector form and explain the terms.
3. Mention the SI unit and dimensional formula of momentum.
4. Distinguish between mass and weight of a body.
5. Write Newton's second law in component form.
6. State and explain Newton’s I law of motion.
7. Mention the significance of component form of Newton's second law.
8. What is an impulsive force? Give example.
9. Define impulse of a force with an example.
10. State and explain Newton's third law of motion.
11. Give an example which illustrates the law of conservation of linear momentum.
12. State the principle of rocket propulsion.
13. Mention the common forces in mechanics.
14. What are normal reaction and friction?
15. What are contact forces? Give examples for contact forces in mechanics.
16. Mention the types of friction.
17. Mention the advantages of friction.
18. Name the types of kinetic friction.
19. What is sliding friction? Give example.
20. What is rolling friction? Give example.
21. What is banking of roads? Why banking is necessary for a curved road?
22. A constant force of 8 N is applied to a body of mass 3 kg. Find the acceleration of the body. [2.66 ms-2]
23. A 10 kg object accelerates at 2 m/s². What is the magnitude of the force? [20 N]
-1
24. A body of mass 1.5 kg has linear moment of 6 kgms . Find its linear velocity. [4 ms-1]

THREE MARK QUESTIONS:

1. Write Galileo's experimental observations of motion of objects on a single inclined plane.
2. Explain (i) inertia of rest, (ii) inertia of motion and (iii) inertia of direction, with example for each.
3. Show that the impulse of a force is equal to the change in momentum produced in the body.
4. Write the important points to be noted about the Newton's third law of motion with regard to the usage
of the terms "action and reaction".
5. What are concurrent forces? Obtain the condition for the equilibrium of the concurrent forces.
6. State the laws of limiting friction.
7. State the laws of kinetic friction.
8. Mention any three disadvantages of friction. OR Friction is an evil. Explain.
9. Mention any three methods of reducing friction.
10. Derive an expression for maximum speed of circular motion of a car on a level road.
11. A body of mass 25 kg moving initially with a speed of 15 ms-1 brought to stop with an average
retardation of 2.5 ms-2. How long does the body take to stop? [6 s]
-1 -1
12. Constant force acting on a body of mass 5 kg changes its speed from 4 ms to 7 ms in two seconds,
the direction of the body remains unchanged. What is the magnitude of force? [7.5 N]
13. Two billiard balls each of mass 0.05 kg moving in opposite directions with speed 6 ms-1 collide and
rebound with the same speed. What is the impulse imparted to each ball due to the other? [– 0.6 Ns]
-1
14. A bullet of mass 0.04 kg moving with a speed of 90 ms enters a heavy wooden and is stopped after a
distance of 0.6 m. What is the average resistive force exerted by the block on the bullet? [– 270 N]

FIVE MARK QUESTIONS:

1. State Newton's second law of motion. Hence, derive the relation ⃗ = ⃗, where symbols have their
usual meaning. OR
State Newton's second law motion. Arrive at an expression for force acting on a particle of mass m
producing in it an acceleration a.
2. State and prove the law of conservation of linear momentum in the case of two colliding bodies. OR
Arrive at the principle of conservation of linear momentum for two bodies colliding while moving
along same straight line.
3. Derive an expression for maximum speed of a car on a banked road in circular motion. OR
Obtain the expression for the maximum speed with which a vehicle can safely negotiate a curved road
banked at an angle θ.
4. A driver of a car moving at 25 ms-1 sees a child on the road 70 m ahead and stops the car 20 m earlier
to the child. If the mass of the car with the driver is 1000 kg, calculate the force exerted by the brakes
on the car and the time taken to stop the car. [6250 N, 4 s]
5. A body of mass 2 kg is acted upon by two perpendicular forces 4 N and 3 N. Calculate the magnitude
and direction of the acceleration of the body. [5 N, 53° 8′ with 4 N force]
6. A machine gun of 15 kg fires 0.02 kg bullets at the rate of 10 per second with a speed of 300 ms-1.
Calculate the force required to hold the gun in position. [60 N]
7. A body of mass 2 kg is placed on a horizontal surface having kinetic friction 0.4 and static friction 0.5.
If the force applied on the body is 18 N, calculate the acceleration of the body. Take g = 10 ms-2.
[5 ms-2]
8. Two masses 8 kg and 12 kg are connected at the two ends of a light inextensible string that goes over a
frictionless pulley. Calculate the acceleration of the masses and the tension in the string when the
masses are released. [1.96 ms-2, 94.08 N]
9. A 70 kg man stands in contact against the inner wall of a hollow cylindrical drum of radius 3 m
rotating about its vertical axis with 200 rev/min. The coefficient of friction between the wall and his
clothing is 0.15. What is the minimum rotational speed of the cylinder to enable the man to remain
stuck to the wall (without falling) when the floor is suddenly removed? [4.7 rad s-1]

ANSWERS TO MULTIPLE CHOICE QUESTIONS:

1 2 3 4 5 6 7 8 9 10 11
B D A C B C B B B D B
12 13 14 15 16 17 18 19 20 21 2
D A C D C C D A B D

ANSWERS TO FIBS:

1. mass 2. constant 3. impulse 4. zero 5. Nm-1

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5. WORK, ENERGY AND POWER

MULTIPLE CHOICE QUESTIONS:

1. The scalar product is given by
(A) A⃗ × B⃗ = AB cosθ (B) A⃗ • B⃗ = AB cosθ
(C) A⃗ • B⃗ = AB sinθ (D) A⃗ × B⃗ = AB sinθ