Read MCQ Questions for Class 11 Physics Chapter 5 Laws of Motion with Answers

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Laws of Motion Class 11 MCQs Questions with Answers

Multiple Choice Type Questions

Question 1.

A man in a train in motion is facing the engine. He tosses a coin up, the coin falls behind him. The train is

(a) moving forward with uniform speed.

(b) moving forward with acceleration.

(c) moving backward with uniform speed.

(d) moving forward with retardation.

Answer

Answer: (b) moving forward with acceleration.


Question 2.

A jet plane flying in atmosphere gets reaction from

(a) gravity

(b) atmosphere

(c) gases ejected by the plane

(d) gravity and atmosphere

Answer

Answer: (c) gases ejected by the plane


Question 3.

A fireman wants to slide down a rope. The breaking load for the rope is (frac 34) th of the weight of the man. With what minimum acceleration should the fireman slide down? Acceleration due to gravity is g.

(a) (frac g4)

(b) (frac g2)

(c) (frac 34) g

(d) zero

Answer

Answer: (a) (frac g4)


Question 4.

Ratio of force and acceleration measures :

(a) inertia

(b) velocity

(c) impulse

(d) momentum

Answer

Answer: (a) inertia


Question 5.

Rocket works on the principle of conservation of:

(a) energy

(b) momentum

(c) mass

(d) All of the above

Answer

Answer: (b) momentum


Question 6.

A bird is sitting in a wire cage hanging from the spring balance. Let the reading of the spring balance be W1. If the bird flies about inside the cage, the reading of the spring balance becomes W2. Which of the following is true?

(a) W1 > W2

(b) W1 2

(c) W1 = W2

(d) None of the above

Answer

Answer: (a) W1 > W2


Question 7.

A heavy log of wood having weight W is having one of its end on the ground and the other on the shoulder of a man. It makes an angle 6 with the horizontal. What is the weight experienced by the man?

(a) W

(b) (frac W2)

(c) W cos θ

(d) W sin θ

Answer

Answer: (b) (frac W2)


Question 8.

A rope of mass m is held vertically by fixing its upper end to a rigid support. What will be the tension in the rope at a distance x from the rigid support? Given that the length of the rope is L and acceleration due to gravity is g.

(a) mg

(b) (frac xL) × mg

(c) (frac L-xL) × mg

(d) (frac LL-x) × mg

Answer

Answer: (c) (frac L-xL) × mg


Question 9.

A body is placed on an inclined plane and has to be pushed down. The angle made by the normal reaction with the vertical will be

(a) equal to the angle of friction

(b) more than the angle of friction

(c) equal to the angle of repose

(d) less than the angle of repose

Answer

Answer: (d) less than the angle of repose


Question 10.

Lubrication reduces friction because

(а) the relative motion is between the liquid and solid.

(b) laws of limiting friction are not applicable.

(c) lubricant molecules act as ball bearings.

(d) none of the above.

Answer

Answer: (а) the relative motion is between the liquid and solid.


Question 11.

A body of mass 5 kg and surface area 18 cm² begins to slide down an inclined plane when the angle of inclination is (frac π6). If the surface area of the same body is made double, keeping the mass unchanged, it will begin to slide down when the angle of inclination is

(а) (frac π3)

(b) (frac π2)

(c) (frac 2π3)

(d) (frac π6)

Answer

Answer: (d) (frac π6)


Question 12.

A jet of water of cross-sectional area ‘a’ strikes a wall at angle θ with the wall and rebounds elastically with the same speed v. If density of water be p, then the normal thrust on the wall will be

(a) av²p sin θ

(b) 2av²p sin θ

(c) 2av²p cos θ

(d) av²p cos θ

Answer

Answer: (b) 2av²p sin θ


Question 13.

Starting from rest, a body slides down a 45° inclined plane in twice the time it takes to slide down the same distance in the absence of friction. The coefficient of friction between the body and the inclined plane is

(а) (frac 12)

(b) (frac 14)

(c) (frac √32)

(d) (frac 34)

Answer

Answer: (d) (frac 34)


Question 14.

A rocket of mass 6000 kg is set for vertical firing, if the exhaust speed be 1 km s-1, the gas must be ejected to give the rocket an upward acceleration of 20 ms-2 is

(a) 120 kg/s

(b) 180 kg s-1

(c) 45 kg/s

(d) 90 kg/s

Answer

Answer: (b) 180 kg s-1


Question 15.

A heavy uniform chain lies on horizontal table top. If the coefficient of friction Between the chain and the table surface be 0.25, then the maximum fraction of the length of the chain that can hang over one edge of the table is

(a) 15%

(b) 20%

(c) 25%

(d) 30%

Answer

Answer: (b) 20%


Question 16.

A car sometimes overturns while taking a turn. When it overturn, it is

(a) the inner wheel, which leaves the ground first

(b) the outer wheel, which leaves the ground first

(c) both the wheels leaves the ground simultaneously

(d) either wheel, which leave the ground first

Answer

Answer: (a) the inner wheel, which leaves the ground first


Question 17.

A disc revolves in a horizontal plane at a steady rate of 3 revolutions per second. A coin just remains on the disc, when it is kept at a distance of 2 cm from the axis of rotation, then the coefficient of friction between the coin and the disc is

(a) 0.5

(b) 0.65

(c) 0.7

(d) 0.75

Answer

Answer: (c) 0.7


Question 18.

A particle just completes motion in a vertical circle of radius r. Its velocity at the highest point is

(a) (sqrt gr)

(b) (sqrt 2gr)

(c) (sqrt 5gr)

(d) None of the above

Answer

Answer: (a) (sqrt gr)


Question 19.

Two weights W1 and W2 are suspended from the ends of a light string passing over a smooth fixed pulley. If the pulley is pulled up at an acceleration g, the tension in the string will be

(a) (frac 4W_1W_2W_1+W_2)

(b) (frac 2W_1W_2W_1+W_2)

(c) (frac W_1W_22(W_1+W_2))

(d) (frac W_1+W_2W_1-W_2)

Answer

Answer: (a) (frac 4W_1W_2W_1+W_2)


Question 20.

A bird dismounts on a stretched telegraph wire. The additional tension produced in the wire is

(a) zero

(b) equal to the weight of the bird

(c) greater than the weight of the bird

(d) less than the weight of the bird

Answer

Answer: (c) greater than the weight of the bird


Question 21.

Which of the following is a self adjusting force?

(a) Limiting friction

(b) Dynamic friction

(c) Sliding friction

(d) Static friction

Answer

Answer: (d) Static friction


Fill in the blanks

Question 1.

According to Newton’s first law of motion, no force is needed to keep a body in motion with ……………… velocity.

Answer

Answer: constant.


Question 2.

Increase in the area of contact ……………… the cohesion between the surfaces.

Answer

Answer: increases.


Question 3.

A horse pulls the cart, the force ……………… makes the cart to move.

Answer

Answer: applied by the ground on the horse.


Question 4

A person standing on the floor of a train running on horizontal rails falls ……………… when it accelerates and falls ……………… when it decelerates.

Answer

Answer: backward, forward.


Question 5.

The apparent weight of a body ……………… in an upward accelerating lift.

Answer

Answer: increases.


Question 6.

A uniform cube of side ‘a’ and mass ‘m’ rests on a rough horizontal table. A horizontal force F is applied normal to .one of the faces at a point that is directly above the centre of the face at a height (frac 34) a above the base. The minimum value of F for which the cube begins to tip about an edge is ……………… (the cube does not slide).

Answer

Answer: (frac 23) mg.


Question 7.

A 3 kg load is suspended vertically by a 6 kg rope. The tension at the upper end of the spring will be ………………

Answer

Answer: 9 kg.


Question 8.

The effect of the force F for a time ∆t is same as the effect of a force 2F for a time ………………

Answer

Answer: (frac ∆t2)


Question 9.

(i) Too much smoothening ……………… friction.

(ii) On the two wheels of a moving cycle, the friction acts in ……………… direction.

Answer

Answer:

(i) increases,

(ii) opposite.


Question 10.

Friction depends upon ……………… of the surfaces in contact and is independent of ……………… of the surfaces in contact.

Answer

Answer: nature and material, area and shape.


True/False Type Questions

Question 1.

If a particle is moving with a constant speed along a straight line, we don’t require a force to keep it moving with uniform velocity.

Answer

Answer: True


Question 2.

An athlete runs some distance before taking a long jump because by running, he gives himself larger inertia of motion.

Answer

Answer: True


Question 3.

A rider on a horse back falls forward, when the horse suddenly stops. This is due to inertia Of rest of the rider.

Answer

Answer: False


Question 4.

A body moving with a constant speed on a horizontal suriace does not have acceleration.

Answer

Answer: True


Question 5.

A body is moving down a long inclined plane 1 in 2. The coefficient of friction between the body and the plane varies as JJ. = 0.49x, where x is the distance moved down the plane. The body will then have its maximum velocity when it reaches the bottom of the plane.

Answer

Answer: True


Question 6.

A stone is thrown from the ground at an inclination of 4. Its horizontal range is then four times the maximum height reached by it.

Answer

Answer: True


Question 7.

It is difficult to run on sand because no frictional force is produced by the sand.

Answer

Answer: False


Question 8.

Essential characteristic of equilibrium is that acceleration is equal to zero.

Answer

Answer: True


Question 9.

A man in a lift weighs more when the lift begins to go up.

Answer

Answer: True


Question 10.

A man is at rest in the middle of a pond on perfectly smooth ice. He can get himself to the shore by making use of Newton’s first law.

Answer

Answer: False


Question 11.

Jet and rocket work on the principle of conservation of linear momentum.

Answer

Answer: True


Question 12.

Rolling friction is lesser than sliding friction.

Answer

Answer: True


Question 13.

Rubber tyre on dry concrete surface has maximum coefficient of friction.

Answer

Answer: True


Question 14.

Sliding contact with road decreases due to proper inflation, of tyres and thus saves fuel.

Answer

Answer: True


Question 15.

While walking on the ice, one should take small steps to avoid slipping. This is because smaller steps ensure larger friction.

Answer

Answer: True


Question 16.

If a ladder is not in equilibrium against a smooth vertical wall, then it can be made in equilibrium by increasing the angle of inclination.

Answer

Answer: True


Question 17.

If a number of forces are acting simultaneously on a particle, then each one of them will produce the same effect which it would have done while acting alone. This is known as principle of physical independence of forces.

Answer

Answer: True


Question 18.

A man is standing on a spring platform. The reading of spring balance is 60 kgf. If man jumps outside from the platform, then the reading of spring balance will first increase and then decrease to zero.

Answer

Answer: True


Question 19.

The angle of banking depends upon the mass of the vehicle.

Answer

Answer: True


Question 20.

When a train moves on an unbanked circular bend of rails, the inner rail wear out faster as the inward pressure on the inner rail is more than that on the outer rail.

Answer

Answer: True


Question 21.

Advantage 6f banking of roads or tracks is that it helps in avoiding skidding of vehicles or trains and one may move without decreasing the speed of the vehicle.

Answer

Answer: True


Question 22.

A plumb line is hahging from the ceiling of a car. When the car is moving along a horizontal track with an acceleration ‘a’, the plunb line gets inclined at an angle tan-1 (a/g).

Answer

Answer: True


Question 23.

During the free fall of the beaker, the upthrust on the wooden block floating in water contained in the beaker is zero because in the state of weightlessness the upthrust is zero.

Answer

Answer: True


Question 24.

The limiting friction depends upon the nature of surfaces in contact.

Answer

Answer: True


Question 25.

When a person walks on a rough surface, the frictional force exerted by the surface on the person is opposite to the direction of his motion.

Answer

Answer: True


Question 26.

Centripetal force is always directed opposite to the centrifugal force.

Answer

Answer: True


Question 27.

A sparrow of weight W flying in the air sits on a stretched telephone wire. The additional tension T produced in the wire is > W.

Answer

Answer: True


Question 28.

A heavy uniform bar of weight W is being carried by two men on their shoulders. If one of them lets it fall from the end carried by him, then weight felt by the other is zero.

Answer

Answer: True


Question 29.

For climbing up a pole, the minimum force of friction should be equal to his weight Le. µR = mg.

Answer

Answer: True


Question 30.

A body is projected upwards with a kinetic energy of400 J. Taking the friction of air into account, when it returns to earth, its K.E. is lesser than 400 J.

Answer

Answer: True


Question 31.

Decrease of coefficient of friction enables us to transport even a heavy barrel by rolling across the road.

Answer

Answer: True


Question 32.

Brakes of very small contact area are not used although friction is independent of area because friction causes wear and tear very fast.

Answer

Answer: True


Question 33.

The fast moving vehicles are given special shapes (streamlined) to reduce wet friction.

Answer

Answer: True


Match the Following

Column I Column II
(a) The line drawn through the point of application of force in its direction (i) gravitational mass
(b) Mass of a body which determines the gravitational pull due to Earth or any other body acting upon it (ii) inertial mass
(c) Ratio of external force to the acceleration produced in the body (iii) 1kg × 1 ms-2
(d) 1 Newton (iv) line of action of force
Answer

Answer:

Column I Column II
(a) The line drawn through the point of application of force in its direction (iv) line of action of force
(b) Mass of a body which determines the gravitational pull due to Earth or any other body acting upon it (i) gravitational mass
(c) Ratio of external force to the acceleration produced in the body (ii) inertial mass
(d) 1 Newton (iii) 1kg × 1 ms-2

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