CBSE Class 11 Physics Laws of Motion Worksheet Set E

Question. A person sitting in an open car moving at constant velocity throws a ball vertically up into air. The ball fall:
a. Outside the car:
b. In the car ahead of the person
c. In the car to the side of the person
d. Exactly in the hand which threw it up
Answer : D

Question. A vehicle of 100 kg is moving with a velocity of 5 m/sec.
To stop it in 1/10 sec, the required force in opposite direction is:
a. 5000 N
b. 500 N
c. 50 N
d. 1000 N
Answer : A

Question. A train is moving with velocity 20 m/sec. on this, dust is falling at the rate of 50 kg/min. The extra force required to move this train with constant velocity will be:
a. 16.66 N
b. 1000 N
c. 166.6 N
d. 1200 N
Answer : A

Question. You are on a frictionless horizontal plane. How can you get off if no horizontal force is exerted by pushing against the surface?
a. By jumping b. By splitting or sneezing
c. By rolling your body on the surface
d. By running on the plane
Answer : B

Question. A weightless ladder, 20 ft long rests against a frictionless wall at an angle of 60o with the horizontal. A 150 pound man is 4 ft from the top of the ladder. A horizontal force is needed to prevent it from slipping. Choose the correct magnitude from the following:

a. 175 lb
b. 100 lb
c. 70 lb
d. 150 lb
Answer : C

Question. Two forces, with equal magnitude F, act on a body and the magnitude of the resultant force is F/3. The angle between the two forces is:
a. cos^-1 (- 17/18)
b. cos^-1 (- 1/3)
c. cos^-1 (2/3)
d. cos^-1 (8/9)
Answer : A

Question. Three forces starts acting simultaneously on a particle moving with velocity v. These
forces are represented in magnitude and direction by the three sides of a triangle ABC (as shown). The particle will now move with velocity:

a. υ remaining unchanged
b. Less than v
c. Greater than v
d. υ in the direction of the largest force BC
Answer : A

Question. The resultant of two forces, one double the other in magnitude, is perpendicular to the smaller of the two forces. The angle between the two forces is:

a. 60º
b. 120º
c. 150º
d. 90º
Answer : B

Question. A mass M is suspended by a rope from a rigid support at P as shown in the figure. Another rope is tied at the end Q, and it is pulled horizontally with a force F. If the rope PQ makes angle θ with the vertical then the tension in the string PQ is:

a. F sinθ
b. F / sinθ
c. F cosθ
d. F / cosθ
Answer : B

Question. If the force on a rocket moving with a velocity of 300 m/s is 210 N, then the rate of combustion of the fuel is
a. 0.7 kg/s
b. 1.4 kg/s
c. 0.07 kg/s
d. 10.7 kg/s
Answer : A

Question. A rocket with a lift-off mass 3.5 × 10⁴ kg is blasted upwards with an initial acceleration of 10 m / s². Then the initial thrust of the blast is
a. 1.75×10⁵ N
b. 3.5×10⁵ N
c. 7.0×10⁵ N
d. 14.0×10⁵ N
Answer : C

Question. A force of 50 dynes is acted on a body of mass 5 g which is at rest for an interval of 3 seconds, then impulse is
a. 0.15 x 10⁻³ N-s
b. 0.98 x 10⁻³ N-s
c. 1.5 x 10⁻³ N-s
d. 2.5 x 10⁻³ N-s
Answer : C

Question. A cricket ball of mass 150 gm is moving with a velocity of 12 m/s and is hit by a bat so that the ball is turned back with a velocity of 20 m/s. The force of blow acts for 0.01s on the ball. The average force exerted by the bat on the ball is:
a. 480 N
b. 600 N
c. 500 N
d. 400 N
Answer : A

Question. In a rocket of mass 1000 kg fuel is consumed at a rate of 40 kg/s. The velocity of the gases ejected from the rocket is 5×10⁴ m/ s. The thrust on the rocket
a. 2×10³ N
b. 5×10⁴ N
c. 5×10⁶ N
d. 5×10⁹ N
Answer : C

Question. A rocket has a mass of 100 kg. 90% of this is fuel. It ejects fuel vapours at the rate of 1 kg/sec with a velocity of 500 m/sec relative to the rocket. It is supposed that the rocket is outside the gravitational field. The initial upthrust on the rocket when it just starts moving upwards is
a. Zero
b. 500 N
c. 1000 N
d. 2000 N
Answer : B

Question. The kinetic energy of two masses m1 and m2 are equal their ratio of linear momentum will be

Answer : C

Question. Three blocks of masses 2 kg, 3 kg and 5 kg are connected to each other with light string and are then placed on a frictionless surface as shown in the figure. The system is pulled by a force F = 10N, then tension T₁ =

a. 1 N
b. 5 N
c. 8 N
d. 10 N
Answer : C

Question. A body of mass 2 kg is hung on a spring balance mounted vertically in a lift. If the lift descends with an acceleration equal to the acceleration due to gravity ‘g’, the reading on the spring balance will be
a. 2 kg
b. (4 × g) kg
c. (2 × g) kg
d. Zero
Answer : D

Question. If the lift in problem, moves up with an acceleration equal to the acceleration due to gravity, the reading on the spring balance will be
a. 2 kg
b. (2 × g) kg
c. (4 × g) kg
d. 4 kg
Answer : D

Question. A ball of mass 150g moving with an acceleration 20 m/s² is hit by a force, which acts on it for 0.1 sec. The impulsive force:
a. 0.5 N-s
b. 0.1 N-s
c. 0.3 N-s
d. 1.2 N-s
Answer : C

Question. A block A of mass 7 kg is placed on a frictionless table. A thread tied to it passes over a frictionless pulley and carries a body B of mass 3 kg at the other end. The acceleration of the system is (given g = 10 ms^–2)

a. 100 ms^–2
b. 3 ms^–2
c. 10 ms^–2
d. 30 ms^–2
Answer : B

Question. The ratio of the weight of a man in a stationary lift and when it is moving downward with uniform acceleration ‘a’ is 3 : 2. The value of ‘a’ is (g- Acceleration due to gravity on the earth)
a. (3/2)g
b. g/3
c. (2/3)g
d. g
Answer : B

Question. Two blocks of mass 4 kg and 6 kg are placed in contact with each other on a frictionless horizontal surface. If we apply a push of 5 N on the heavier mass, the force on the lighter mass will be

a. 5 N
b. 4 N
c. 2 N
d. None of the above
Answer : C

Question. In the above problem, if a push of 5 N is applied on the lighter mass, the force exerted by the lighter mass on the heavier mass will be
a. 5 N
b. 4 N
c. 2 N
d. None of the above
Answer : D

Question. In the above problem, the acceleration of the lighter mass will be
a. 0.5 m s^–2
b. 5/4 m s^–2
c. 5/6 m s^–2
d. None of the above
Answer : A

Question. A 60 kg man stands on a spring scale in the lift. At some instant he finds, scale reading has changed from 60 kg to 50 kg for a while and then comes back to the original mark. What should we conclude?
a. The lift was in constant motion upwards
b. The lift was in constant motion downwards
c. The lift while in constant motion upwards, is stopped suddenly
d. The lift while in constant motion downwards, is suddenly stopped
Answer : C

Question. A 20 kg block is initially at rest on a rough horizontal surface. A horizontal force of 75 N is required to set the block in motion. After it is in motion, a horizontal force of 60 N is required to keep the block moving with constant speed. The coefficient of static friction is
a. 0.38
b. 0.44
c. 0.52
d. 0.60
Answer : A

Question. Two blocks are in contact on a frictionless table one has a mass m and the other 2 m as shown in figure. Force F is applied on mass 2m then system moves towards right.
Now the same force F is applied on m. The ratio of force of contact between the two blocks will be in the two cases respectively.

a. 1 : 1
b. 1 : 2
c. 1 : 3
d. 1 : 4
Answer : B

Question. A sphere is accelerated upwards with the help of a cord whose breaking strength is five times its weight. The maximum acceleration with which the sphere can move up without cord breaking is
a. 4g
b. 3g
c. 2g
d. g
Answer : A

Question. A block of mass M is placed on a rough floor of a lift. The coefficient of friction between the block and the floor is μ.
When the lift falls freely, the block is pulled horizontally on the floor. What will be the force of friction
a. μ Mg
b. μ Mg/2
c. 2μ Mg
d. None of these
Answer : D

Question. A body of 5 kg weight kept on a rough inclined plane of angle 30º starts sliding with a constant velocity. Then the coefficient of friction is (assume g = 10 m/s²)
a. 1 /√3
b. 2 /√3
c. √3
d. 2√3
Answer : A

Question. A man is standing on a weighing machine placed in a lift, when stationary, his weight is recorded as 40 kg. If the lift is accelerated upwards with an acceleration of 2m/ s², then the weight recorded in the machine will be (g = 10m/ s²)
a. 32 kg
b. 40 kg
c. 42 kg
d. 48 kg
Answer : D

Question. In the above problem, given that M₁ = M₂ and θ = 30º. What will be the acceleration of the system?
a. 10 m s^–2
b. 5 m s^–2
c. 2.5 m s^–2
d. Zero
Answer : C

Question. In the above problem, given that M₁ = M₂ = 5 kg and θ = 30º .What is tension in the string?
a. 37.5 N
b. 25 N
c. 12.5 N
d. Zero
Answer : A

Question. If a ladder weighing 250N is placed against a smooth vertical wall having coefficient of friction between it and floor is 0.3, then what is the maximum force of friction available at the point of contact between the ladder and the floor
a. 75 N
b. 50 N
c. 35 N
d. 25 N
Answer : A

Question. A block of mass 10 kg is placed on a rough horizontal surface having coefficient of friction μ = 0.5. If a horizontal force of 100 N is acting on it, then acceleration of the block will be
a. 0.5 m/s²
b. 5 m/s²
c. 10 m/s²
d. 15 m/s²
Answer : B

Question. A body of weight 64 N is pushed with just enough force to start it moving across a horizontal floor and the same force continues to act afterwards. If the coefficients of static and dynamic friction are 0.6 and 0.4 respectively, the acceleration of the body will be (Acceleration due to gravity = g)
a. g/6.4
b. 0.64 g
c. g/32
d. 0.2 g
Answer : D

Question. A body of mass 10 kg is lying on a rough plane inclined at an angle of 30º to the horizontal and the coefficient of friction is 0.5. The minimum force required to pull the body up the plane is
a. 914 N
b. 91.4 N
c. 9.14 N
d. 0.914 N
Answer : B

Question. On the horizontal surface of a truck (μ = 0.6), a block of mass 1 kg is placed. If the truck is accelerating at the rate of 5m/sec² then frictional force on the block will be
a. 5 N
b. 6 N
c. 5.88 N
d. 8 N
Answer : A

Question. The upper half of an inclined plane of inclination θ is perfectly smooth while the lower half is rough. A body starting from the rest at top comes back to rest at the bottom if the coefficient of friction for the lower half is given
a. μ = sin θ
b. μ = cot θ
c. μ = 2 cos θ
d. μ = 2 tan θ
Answer : D

Question. What is the maximum value of the force F such that the block shown in the arrangement does not move (μ =1/ 2√3)

a. 20 N
b. 10 N
c. 12 N
d. 15 N
Answer : A

Question. A man weighs 80kg. He stands on a weighing scale in a lift which is moving upwards with a uniform acceleration of 5 m/s². What would be the reading on the scale. (g = 10m/s ²)
a. 400 N
b. 800 N
c. 1200 N
d. Zero
Answer : C

Question. A block of mass 1 kg slides down on a rough inclined plane of inclination 60º starting from its top. If the coefficient of kinetic friction is 0.5 and length of the plane is 1 m, then work done against friction is (Take g = 9.8 m/s²)
a. 9.82 J
b. 4.94 J
c. 2.45 J
d. 1.96 J
Answer : C

Question. If a block moving up at θ = 30° with a velocity 5 m/s, stops after 0.5 sec, then what is μ
a. 0.5
b. 1.25
c. 0.6
d. None of these
Answer : C

Question. A body of mass 5kg rests on a rough horizontal surface of coefficient of friction 0.2. The body is pulled through a distance of 10m by a horizontal force of 25 N. The kinetic energy acquired by it is (g = 10 ms²)
a. 330 J
b. 150 J
c. 100 J
d. 50 J
Answer : B

Question. 300 Joule of work is done in sliding a 2 kg. block up an inclined plane to a height of 10 meters. Taking value of acceleration due to gravity ‘g’ to be 10 m/s², work done against friction is
a. 100 J
b. 200 J
c. 300 J
d. Zero
Answer : A

Question. Two masses m1 and m2 are attached to a string which passes over a frictionless smooth pulley. When m₁ = 10 kg, m₂ = 6 kg, the acceleration of masses is
a. 20 m / s²
b. 5 m / s²
c. 2.5 m / s²
d. 10 m / s²
Answer : C

Question. In the above problem, given that M₂ = 2M1 and the tension in the string is T. If the positions of the masses are reversed, the tension in the string will be
a. 4 T
b. 1 T
c. T
d. T/2
Answer : C

Question. A block of mass m rests on a rough horizontal surface as shown in the figure.

Coefficient of friction between the block and the surface is μ. A force F = mg acting at angle θ with the vertical side of the block pulls it. In which of the following cases the block can be pulled along the surface
a. tanθ ≥ μ
b. cotθ ≥ μ
c. tan θ / 2 ≥ μ
d. cotθ / 2 ≥ μ
Answer : D

Question. A block of mass 50 kg slides over a horizontal distance of 1 m. If the coefficient of friction between their surfaces is 0.2, then work done against friction is
a. 98 J
b. 72J
c. 56 J
d. 34 J
Answer : A

LAWS OF MOTION

SECTION – A CONCEPTUAL AND APPLICATION TYPE QUESTIONS

1. If the net force acting on the body be zero, will the body remain necessarily in rest position ? Explain your answer .

2. 1. Action and reaction forces do not balance each other . why ? 

3. 2. If a force is acting on a moving body perpendicular to the direction of motion , then what will be its effect on the speed and direction of the body ?

4. 3. Is the linear momentum of a ball falling freely conserved ? why ? 

5. 4. Why passengers are thrown forward from their seats when a speeding bus stops suddenly ?

6. 6. Why are the passengers thrown outwards when a car in which they are travelling suddenly takes a circular turn ?

7. 7. Show that if the net force acting on a particle is zero, its momentum will remain unchanged . 

8. 8. A cricket player lower his hands to catch the ball safely . Explain why ? 

9. It is easy to catch a table tennis ball than a cricket ball even both are moving with same velocity . why ?

10. Can a bomb initially at rest explodes into three pieces which fly in mutually perpendicular directions ?

11. While firing a bullet , the gun should be held tight to the shoulder .Why ? 

12. What is the principle of working of a rocket ? 

13. Carts with rubber tyres are easier to ply than those with iron wheels .why ? 

14. On what factors does the coefficient of friction depend ? 

15. A horse has to apply more force to start a cart than to keep it moving . Why ? 

16. Proper inflation of tyres of vehicles save fuel . Why ? 

17. What is the angle between frictional force and instantaneous velocity of the body moving over a rough surface ?

18. Does the angle of banking depend on the mass of vehicle ?

19. Why does a cyclist bend inwards while riding along a curved road ? 

20. A lift is going up with an acceleration 3g . A man is inside the lift and his mass is m . What will be the reaction of the floor on the man ?
 

SECTION – B NUMERICAL PROBLEMS

1. 1. A truck starts from rest and rolls down a hill with constant acceleration . It travels a distance of 400 m in 20 s . Calculate the acceleration of the truck and force acting on it , if its mass is 7 metric ton .

2. A car of mass 1000 kg is moving with a velocity of 10 m/s and is acted upon by a forward force of 1000 N due to engine and retarding force of 500 N due to friction . What will be the velocity after 10 seconds ?

3. A machine gun fires a bullet of mass 40 g with a speed of 1200 m/s . The person holding the gun can exert a maximum force of 144 N on it . What is the number of bullets that can be fired from the gun per second ?

4. A golf ball of mass 60 g at rest is hit with a striker . Find the impulse of the hit if the ball stops after travelling a horizontal distance of 50 m with a uniform retardation of 4 ms-2.

5. 2. A shell of mass 0.02 kg is fired by a gun of mass 10 kg . If the muzzle speed of the shell is 80 m/s , what is the recoil speed of the gun ?

6. Two billiard balls each of mass 50 g moving in opposite directions with a speed of 36 km/hr collide and rebound with the same velocity . What is the impulse imparted to each ball due to the other ?

7. A mass of 6 kg is suspended by a rope of 2m from a ceiling. A force of 50 N in the horizontal direction is applied at the midpoint of the rope . What is the angle the rope makes with the vertical in equilibrium ?

8. The initial speed of a body of mass 2 kg is 5 m/s . A force acts for 4 s in the direction of motion of the body . The force – time graph is as shown. Calculate the impulse of the force and the final speed of the body .

9. A ball moving with a momentum of 5 kg m /s strikes against a wall at an angle of 45 ^o and rebounds at the same angle . Calculate the change in momentum.

10. A bomb at rest explodes into three fragments of equal masses. Two fragments fly off at right angles to each other with velocities 9 m/s and 12 m/s respectively . Calculate the speed of the third fragment .

11. An elevator and its load weigh a total of 800 kg . Find the tension T in the supporting cable when the elevator ,originally moving downwards at 20m/s is brought to rest with constant retardation in a distance of 50 m. g = 10ms^-2

12. Two bodies of masses 4 kg and 3 kg respectively are connected by a light string passing over a smooth frictionless pulley. Calculate the acceleration of the masses and tension in the string.

13. A body of mass 10 kg is sliding down a rough inclined plane which makes an angle of 30 ⁰ with the horizontal . If the coefficient of friction is 0.25 ,find the acceleration of the body ? g = 10 m/s²

14. A circular race track of radius 400 m is banked at an angle of 10 o . If the coefficient of friction between the wheels of a race car and the road is 0.2 , what is the
 (i) optimum speed of the car to avoid wear and tear on its tyres
 (ii) maximum permissible speed to avoid slipping . g = 9.8 m/s2

15. A wooden block of mass 2 kg rests on a soft horizontal floor. When an iron cylinder of mass 25 kg is placed on top of the block , the floor yields steadily and the block and the cylinder together go down with an acceleration of 0.1 m/ s² . What is the action of the block on the floor

(a) before
(b) after the floor yields ? g = 10 m/s².

16. A train is moving along a horizontal track . A pendulum suspended from the roof makes an angle of 4 o with the vertical. Obtain the acceleration of the train . g = 10 m/s²

17. A body of mass 10 kg is placed on a smooth horizontal table . It is connected to a string which passes over a frictionless pulley and carries at the other end , a body of mass 5 kg . Calculate the acceleration of the masses and tension in the string.

18. A mass of 200 kg is resting on a rough inclined plane of 30 ^o . If the coefficient of friction is 1/√3, find the least and the greatest forces acting parallel to the plane to keep the mass in
equilibrium.

19. An aircraft executes a horizontal loop at a speed of 720 km/hr with its wings banked at 15 ^o . What is the radius of the loop ? g = 10 m/s²

20. A box of mass 4 kg rests upon an inclined plane . The inclination of the plane to the horizontal is gradually increased . It is found that when the slope of the plane is 1 in 3, the box starts sliding down the plane . Given g = 9.8 m/s²

(i)Find the coefficient of friction between the box and the plane .
(ii)What force applied to the box parallel to the plane will just make it move up the plane ?

21. A ball of mass 0.1 kg is suspended by a string 30 cm long . Keeping the string always taut, the ball describes a horizontal circle of radius 15 cm. Calculate the angular speed .

22. Determine the tensions T₁ and T₂ in the strings shown in figure.

23. The pulleys and strings shown in the figure are smooth and of negligible mass. For the system to remain in equilibrium, what should be the angle θ ?

Please click on below link to download CBSE Class 11 Physics Laws of Motion Worksheet Set E