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1Class-VII Physics Question Bank

2 FORCE AND MOTION

I. Tick (✔✔✔✔✔) the most appropriate answer.1. A book lying on a table is an xample of

(a) a body in motion(b) a body at rest(c) a body neither at rest nor in motion(d) none of these

2. A car moving on a straight road is an example of(a) oscillatory motion (b) rotatory motion(c) rectilinear motion (d) periodic motion

3. The kind of motion that a pendulum has is(a) curvilinear (b) rotatory (c) oscillatory (d) rectilinear

4. An example of curvilinear motion is(a) an apple falling from a tree (b) a spinning wheel(c) the motion of a pendulum (d) throwing of a javelin

5. A person driving a car is in a state of rest with respect to(a) a post box on the roadside (b) a hospital(c) the roof of the car (d) a hoarding on the road

6. The time taken by the bob of a pendulum to complete one oscillationis called its(a) amplitude (b) time period (c) frequency (d) oscillation

7. Distance is a(a) scalar quantity (b) vector quantity(c) normal quantity (d) none of these

8. The quantity which tells the distance of an object travels in a certaintime is called(a) acceleration (b) speed (c) velocity (d) none of these

9. It two bodies are moving with the same speed but in differentdirections, they will have(a) same velocities (b) same acceleration


(c) different velocities (d) none of these10. A body moving with a constant velocity will have

(a) constant acceleration (b) constant retardation(c) zero acceleration (d) none of these

11. A wooden bench lying in the corner of a garden is an example of(a) body in motion(b) body in rest(c) body neither in state of rest nor motion(d) none of these

12. A body moving at a uniform velocity of 2 ms–1 will have(a) uniform acceleration (b) non-uniform acceleration(c) zero acceleration (d) none of these

13. The unit of frequency of pendulum is(a) metre (b) second (c) hertz (d) none of these

14. The time taken by a freely suspended pendulum to complete oneoscillation is(a) amplitude (b) frequency (c) time period (d) none of these

15. A person sitting in a speeding train is at rest with respect to(a) trees (b) fields(c) buildings (d) other passengers

16. The rate of change of velocity is known as(a) speed (b) displacement(c) acceleration (d) none of these

17. When a drill bores a hole in a piece of wood, it describes(a) rotatory motion(b) translatory motion(c) curvilinear motion(d) rotatory and translatory motion

18 A freely falling stone has(a) uniform speed (b) uniform velocity(c) uniform acceleration (d) uniform motion

19. The motion described by the string of violin is(a) oscillatory motion (b) vibratory motion


(c) non-periodic motion (d) rectilinear motion20. With the increase in length of a simple pendulum, its time period

(a) increases (b) decreases(c) remains same (d) none of these

Ans. 1. (b) 2. (c) 3. (c) 4. (d) 5. (c) 6. (b)7. (a) 8. (b) 9. (a) 10. (c) 11. (b) 12. (c)

13. (c) 14. (c) 15. (d) 16. (c) 17. (d) 18. (c)19. (b) 20. (a)

II (A). Fill in the blanks.1. A tree in a park is in state of ______________.2. The earth is in state of ______________.3. A spinning top has a ______________ motion.4. Motion of the earth around the sun is ______________.5. The frequency of a second’s pendulum is ______________.6. The ______________ of a simple pendulum is directly proportional

to the square root of its length.7. The maximum displacement of the bob from its mean position is

called its ______________.8. The ______________ travelled by a moving body is the actual

lenght of the path covered by it.9. When a satellite completes one revolution, the displacement of the

satellite is ______________.10. The SI unit of speed is______________.

Ans. 1. rest 2. motion 3. rotatory4. periodic 5. 0.5 Hz 6. time period7. amplitude 8. distance 9. zero

10. metre per second

II (B). Fill in the blank spaces by choosing correct words from the listgiven below.

List : increases, speed, rectilinear, gravity, curvilinear, acceleration,rotation, velocity, translation, periodic, oscillatory.

1. A moving carrom board coin describes a motion of __________.


2. A ball thrown upwards at an angle describes ______________moton.

3. A wheel of a moving bicycle describes a motion of ____________and motion of ______________.

4. The motion described by a simple pendulum is ______________motion.

5. A motion which repeats itself after a fixed interval of time is called______________ motion.

6. The rate of change of motion is called ______________.7. The rate of change of motion in a specified direction is called

______________.8. The rate of change of velocity is called ______________.9. The acceleration due to ______________ 9.8 ms–2.

10. The time period of a simple pendulum ______________ with theincrease in the length of pendulum.

Ans. 1. rectilinear 2. curvilinear 3. translation, rotation4. oscillatory 5. periodic 6. speed7. velocity 8. acceleration 9. gravity

10. increases

III (A). The statements given below are incorrect. Write correct statement.1. A ball thrown by a boy from a roof-top has oscillatory motion.

Ans. A ball thrown by a boy from a roof-top has rectilinear motion.2. A motion which repeats itself after a fixed interval of time is called

vibratory motion.Ans. A motion which repeats itself after a fixed interval of time is called

periodic motion.3. The length of a second’s pendulum at a place, where g = 9.8 ms–2, is

90.2 cm.Ans. The length of a second’s pendulum at a place, where g = 9.8 ms–2,

is 99.2 cm.4. If the value of g decreases, the time period of the simple pendulum

decreases.Ans. If the value of g decreases, the time period of the simple pendulum


increases.5. The unit of frequency is decibel.

Ans. The unit of frequency is hertz.6. Displacement is a scalar quantity.

Ans. Displacement is a vector quantity.7. Velocity is the distance travelled by a moving body per unit time.

Ans. Speed is the distance travelled by a moving body per unit time.8. The SI unit of acceleration is m/s.

Ans. The SI unit of acceleration is m/s2.9. A body can change its state of rest or of uniform motion on its own.

Ans. A body cannot change its state of rest or of uniform motion on itsown.

10. With the decrease in length of a simple pendulum, its time periodincreases.

Ans. With the increase in length of a simple pendulum, its time periodincreases.

11. The motion described by the needle of a sewing machine is a vibratorymotion.

Ans. The motion described by the needle of a sewing machine is oscillatorymotion.

12. The motion of a bus going around a traffic roundabout is a rotatorymotion.

Ans. The motion of a bus going around a traffic roundabout is a curvilinearmotion.

13. The time period of a second’s pendulum is 1 second.Ans. The time period of a second’s pendulum is 2 second.

14. A runner, running along a circular track at a constant speed has auniform velocity.

Ans. A runner, running along a circular track at a constant speed has anon-uniform velocity.

15. The beating of heart of a healthy person at rest, is a non-periodicmotion.

Ans. The beating of heart of a healthy person at rest, is a periodic motion.


16. The moon waxes and wanes while going around the earth, and hence,it has circular motion.

Ans. The moon waxes and wanes while going around the earth, and hence,it has periodic motion.

17. The motion described by the string of a violin is oscillatory motion.Ans. The motion described by the string of a violin is vibratory motion.

III (B). Write true or false for each statment given below.1. The motion of a giant wheel is a circular motion.2. The motion of the moon around the earth is a curvilinear motion.3. The average acceleration due to gravity is 8.9 ms–2.4. The units of speed and velocity are same in SI system.5. The rate of change of velocity is called speed.6. The motion described by wire of sitar is a vibratory motion.7. The time period of a pendulum increases with the decreases in length.8. A second’s pendulum can be used as a timing device.

Ans. 1. True 2. False 3. False 4. True 5. False6. True 7. False 8. False

IV. Find the odd-one out. Give reasons for your choice.1. Tree, hut, earth, dustbin, chair

Ans. Earth — because it is in the state of motion while others are in thestate of rest.

2. Length of the pendulum, acceleration due to gravity, mass of thebob

Ans. Mass of the bob — because the time period of a pendulum does notdepend on the mass of the bob.

3. Apple falling from a tree, car moving on a straight road, coins movingover a carrom board, giant wheel

Ans. Giant wheel — because it is the example of rotatory motion whileothers are examples of rectilinear motion.

4. Displacement, veleocity, acceleration, weight, speedAns. Speed — because it is the scalar quantity while others are vector

quantities.


5. Aeroplane, bird, lion, fish, submarineAns. Lion — because its movement is neither in air nor in water.

6. Length, time period, frequency, accelerationAns. Frequency — because the term is not used to find the time period

of a freely oscillating pendulum.7. Speeding train on a straight railway line, a freely falling stone, coins

moving over carrom board, a girl on a swingAns. A girl on a swing — because it is an example of a periodic motion

while others are examples of rectilinear motion.8. Velocity, speed, acceleration, mass

Ans. Mass — because other terms are related to the motion.

V. Give reasons for the following.1. Rotation of the earth is a periodic motion.

Ans. A motion which repeats itself at regular intervals of time is calledperiodic motion since the earth rotates about its axis and alwaystakes same time that is 24 hours to complete one round hencerotation of the earth is a periodic motion.

2. A boy riding on a moving bicycle has a multiple motion.Ans. A boy riding on a moving bicycle has a multiple motion because

the wheels of the bicycle rotates to cause rotatory motion and at thesame time the bicycle moves forward in a straight line or curvedpath to cause translatory motion.

VI. Match the following.Physical Quantity SI Unit

1. displacement (a) second2. velocity (b) metre per second square3. time (c) metre per second4. acceleration (d) metre

Ans. 1. (d), 2. (c), 3. (a), 4. (b)

VII. Differntiate between the following.1. Rectilinear motion and curvilinear motion

Ans. Translatory motion along a stright line is called rectilinear motion


while translatory motion along a curved line is called curvilinearmotion.

2. Vibratory motion and periodic motionAns. The motion in which a certain part or parts of a body always remain

fixed and do not move while the rest of the body moves to-and-froin a definite style is called vibratory motion.A motion which repeats itself at regular intervals of time is calledperiodic motion.

3. Scalar quantity and vector quantityAns. A physical quantity which is described completely by its magnitude

is called a scalar quantity.A physical quantity which is described completely by its magnitudeas well as direction is called a vector quantity.

4. Distance and displacementAns. The actual length of a path covered by a moving body, irrespective

of its direction, is called the distance travelled by the body. It is ascalar quantity.The shortest distance covered by a moving body in between twopoints in a particular direction is called its displacement. It is a vectorquantity.

5. Speed and velocityAns. The distance travelled by a moving body per unit time is called its

speed. It is a scalar quantity.The distance travelled by a body per unit time in a given directionis called its velocity. It is a vector quantity.

VIII. Define the following terms and also give one example of each.1. Random motion

Ans. Random motion: A body which has a particular motion thatsuddenly changes to another kind of motion is said to have randommotion. For example, when a mosquito is in flight, at one momentit may have translatory motion, at the next moment it may haverotatory motion. Such a motion is called random motion.

2. Multiple motion


Ans. Multiple motion: Sometimes an object possesses two or moretypes of motion at the same time. Such motion is called multiplemotion. For example, when a spin bowler delivers a ball the ball hasa motion of spin (rotatory motion) while it moves towards thebatsman (translatory motion).

3. Second’s pendulumAns. Second’s pendulum: A pendulum which completes its one oscillation

in two seconds is known as a second’s pendulum. The length of asecond’s pendulum at a place where g = 9.8 m/s2 is 99.2 cm. Asecond’s pendulum is independent of amplitude. Its frequency

n = 12

Hz

IX. Answer these questions.1. What is oscillatory motion? Give two examples.

Ans. A motion in which the body as a whole moves to-and-fro about itsmean position is called oscillatory motion.Examples — The motion of a swing.

The motion of pendulum of a clock.2. What is translatory motion? Name two kinds of translatory motion.

Ans. If an object moves in a line in such a way that every point on theobject moves through the same distance in the same interval of timethe motion of the object is called translatory motion.Examples — A ball rolling on the ground.

A stone falling freely from the roof of a building.3. Give an example to show that rest and motion are relative terms.

Ans. Imagine you are travelling by a train. You are in motion in relationto a farmer standing in a field or trees on the platform because yourposition is changing with respect to them. However, if you compareyour position with respect to the things inside the train, that is otherpassangers, walls, fans, etc. it is not changing. Therefore, in relationto these objects you are at rest, thus, an object can be in motion inrelation to one set of objects while it is at rest in relation to anotherset of objects. We can say that rest and motion are relative terms. It


is the observer and the surroundings that decide whether a givenobject is considered at rest or in motion.

4. What is a simple pendulum? What are the factors affecting the timeperiod of a simple pendulum?

Ans. Simple pendulum. A simple pendulum consists of a small metalball (called bob) suspended by a long thread from a rigid support.Such that the bob is free to swing back and forth.The time period of a simple pendulum depends upon the followingfactors.1. Length. The time period of a simple pendulum is directlyproportional to the square root of its length

T ∝ l2. Aceleration due to gravity. The time period of a simple pendulumis inversely proportional to the square root of the acceleration dueto gravity at that place

T 1∝g

3. Mass of the bob. The time period of a simple pendulum isindependent of the mass of the bob, that is, if we use bobs of differentmasses its time period does not change.4. Nature of the material of the bob. The time period of a simplependulum is independent of the nature of the material of the bob.

5. Classify the following into translatory, rotatory and oscillatorymotions.(a) ball thrown by a child (b) giant wheel(c) piston of a car (d) swinging pendulum(e) freely falling stone (f) spinning top(g) charkha (h) throwing of a javelin(i) potter’s wheel

Ans. (a) Ball thrown by a child — Translatory motion(b) Giant wheel — Rotatory motion(c) Piston of a car — Oscillatory motion(d) Swinging pendulum — Oscillatory motion


(e) Freely falling stone — Translatory motion(f) Spinning top — Rotatory motion(g) Charkha — Rotatory motion(h) throwing of a javelin — Translatory motion(i) Potter’s wheel — Rotatory motion

6. By giving at least two examples each, define the following terms.(a) Rectilinear motion (b) Curvilinear motion(c) Rotatory motion (d) Oscillatory motion(e) Vibratory motion (f) Periodic motion

Ans. (a) Rectilinear motion. When an object moves along a straightline, its motion is called rectilinear motion.Examples – A ball rolling on the ground

A car moving on a straight road.(b) Curvilinear motion. If an object moves along a curved path itsmotion is called curvilinear motion.Examples – A stone thrown by a boy

A car moving along a curved path(c) Rotatory motion. A body is said to be in rotatory motion if itmoves about a fixed axis without chaning its position.Examples – The motion of the blades of a fan

A giant wheel(d) Oscillatory motion. A motion in which the body as a wholemoves to-and-fro about its mean position is called oscilltory motion.Examples – The motion of a swing

The pendulum of a clock(e) Vibratory motion. The motion in which a certain part or partsof a body always remain fixed and do not move, while rest of thebody moves to-and-fro in a definite style is called vibratory motion.Examples – A string of a guitar or a sitar when plucked starts

vibrating.During breathing, our chest expands and contractsthis motion is vibratory in nature.

(f) Periodic motion. A motion which repeats itself at regular intervals


of time is called periodic motion.Examples – The motion of the earth around the sun

The needle of a sewing machine7. Define : (i) rest, (ii) motion.

Ans. (i) Rest – A body is said to be at rest, if it does not change itsposition with respect to a fixed point in its surroundings. For example— a book lying on a table.(ii) Motion – A body is said to be in motion, if it changes its positionwith respect to a fixed point in its surroundings. For examples, aman walking on the road.

8. Define : (a) speed, (b) velocity. Bring out clearly the differencebetween speed and velocity.

Ans. (a) Speed – The distance travelled by a moving body per unit timeis called its speed.(b) Velocity – The distance travelled by a body per unit time in agiven direction is called its velocity.Speed is a scalar quantity whereas velocity is a vector quantity.

9. (a) Define : (i) acceleration, (ii) acceleration due to gravity.Ans. (i) Acceleration – The rate of change of velocity of a body is

called its accleration.

acceleration = change in velocity

time takenThe SI unit of acceleration is meter per second square (m/s2)(ii) Acceleration due to gravity – The acceleration with which abody falls freely towards the earth is called acceleration due to gravity.It is denoted by the symbol ‘g’.The numerical value of acceleration due to gravity is 9.8 m/s2. Thisvalue changes from place to place and at the same place it changeswith altitude.

10. What do you understand by the terms (a) uniform velocity, (b)variable velocity? Give one example of each.

Ans. (a) Uniform velocity – When a body covers equal distances inequal interval of time in a specified direction the body is said to be


moving with a uniform velocity.Example – Imagine a car is moving along a straight road towardseast, such that in every one second it covers a distance of 5 m. Insuch a case, the uniform velocity of car is 5 m/s east.(b) Variable velocity – When a body covers unequal distances inequal intervals of time in a specified direction or equal distances inequal intervals of time, but its direction changes, then the body issaid to be moving with a variable velocity.Example – Consider a body starting from point A and reaches B, Cand D straight towards east in the time intervals of 1 second each.Let the distances covered be 3m, 4m and 2m respectively.

As the body is covering unequal distances in equal intervals of timein a specified direction, therefore, the body is moving with variablevelocity.

11. Prove : v = u + at, where ‘u’ is the initial velocity, ‘v’ is the finalvelocity, ‘a’ is the acceleration and ‘t’ is the time.

Ans. Let us consider a body having an initial velocity u. After time t, thebody moves with a velocity v.From the definition of acceleration, we get

Acceeleration =change in velocity

time taken

=final velocity � initial velocity

time taken

a =v u

t �

at = v – uor, v = u + at

12. Define the following with reference to simple pendulum:


(a) pendulum (b) mean position(c) oscillation (d) time period(e) amplitude

Ans. (a) Pendulum – A small metallic bob (brass or any other material)tied to a light, cotton thread and suspended from a rigid point, suchthat it is free to oscillate about its mean position is called a pendulumor simple pendulum.(b) Mean position – When a freely suspended pendulum is at restthen this position is called mean position or rest position.(c) Oscillation – The complete to and fro motion of a freelyoscillating pendulum about its mean position is called oscillation.(d) Time period – The time taken by a freely oscillating pendulumto complete one oscillation is called time period. Its SI unit is second.(e) Amplitude – The maximum displacement of a pendulum fromits mean position is called amplitude.

13. What is a second’s pendulum? What is the length of second’spendulum.

Ans. A simple pendulum whose time period is 2 second is called second’spendulum.The length of a second’s pendulum at a place where g = 9.8 m/s2 is99.2 cm. A second’s pendulum is independent of amplitude. Itsfrequency n = ½ Hz

14. The length of second’s pendulum is shortened by 20 cm. How thischange in length will affect the time period of the pendulum?

Ans. The time period of a freely oscillating pendulum is given by the

expression T = 2� lg

Where ‘T’ is the time period in seconds, ‘l’ the length of thependulum and ‘g’ the acceleration due to gravity at a given place.From the above expression it is clear that T ∝ l i.e. as the lengthof a pendulum increases, so will increase its time period and viceversa.Therefore, if the length of second’s pendulum is shortened by 20


cm its time period will also shortened.15. What is meant by the term retardation? Name its SI unit.

Ans. If the velocity of a body is decreasing with respect to time, theacceleration is said to be negative. This negative acceleration iscalled retardation.The SI unit of retardation is meter/second2 (m/s2).

X. Practice for numerical problems.1. Calculate the speed of a car moving a distance of 150 km in

3 hours.Ans. Distance (D) = 150 km

Time (t) = 3 hours

Speed (S) =Distance (D)

Time (t) = 150 km3 hours = 50 km/h

2. Calculate the time taken by a train moving at a speed of 50 km/h if itcovers 250 kilometres.

Ans. Speed (S) = 50 km/hDistance (D) = 250 km

Time (t) =Distance (D)

Speed (S) = 250 km50 km/h

= 5 h

3. Calculate the distance travelled by a bicycle moving at a speed of 20km/h in 2 hours.

Ans. Speed (S) = 20 km/hTime (t) = 2 hours

Distance = speed (S) × time (t)= 20 km / h × 2 h= 40 km

4. A car starting from rest, picks up a velocity of 15 m/s in 20 seconds.Find the acceleration of the car.

Ans. Initial velocity (u) = 0Final velocity (v) = 15 m/s

Time (t) = 20 s

Acceleration (a) =v u

t �

= 15 � 0

20 m/s2


=1520 m/s2

= 0.75 m/s2

5. A car is travelling at 15 m/s. If its velocity increases to 20 m/s in 5 sthen find the acceleration of the car.

Ans. Initial velocity (u) = 15 m/sFinal velocity (v) = 20 m/s

Time (t) = 5 s


t �

= 20 � 15

5 m/s2

= 1 m/s2

6. A scooter is travelling with a certain speed. Its final velocity becomes30 m/s in 5 s accelerating at the rate of 2 m/s2. Find its initial velocity.

Ans. Let the initial velocity = uFinal velocity (v) = 30 m/s

Time (t) = 5 sAcceleration (a) = 2 m/s2


t �

2 =30 �

5u

or, 10 = 30 – uor, u = 20 m/s

7. A car is travelling at 20 m/s. If its velocity increases to 30 m/s whileaccelerating at the rate of 5 m/s2, find the time taken to accelerate.

Ans. Let the time taken be t secondsInitial velocity (u) = 20 m/sFinal velocity (v) = 30 m/s

Acceleration (a) = 5 m/s2 5 Time (t) = ?


t �


5 =30 � 20

t

or, t =105 = 2 seconds

8. A scooter is travelling at 10 m/s. Find its velocity if the scooter isaccelerating at the rate of 2 m/s2 in 7 s.

Ans. Let the final velocity be v m/sInitial velocity (u) = 10 m/s

Acceleration (a) = 2 m/s2

Time (t) = 7 s


t �

2 =v � 10

7or, 14 = v – 10or, v = 24 m/s

9. Draw a velocity-time graph of a moving car from the data given inthe following table. Also indicate the acceleration in the graph.velocity (m/s) 0 5 10 15 20 25 30 35 40time (s) 0 1 2 3 4 5 6 7 8

Ans.

The slope of the graph AC gives the acceleration of the body.


10. A horse runs a distance of 1200 metres in 3 min and 20 seconds,what is the speed of the horse.

Ans. Distance (D) = 1200 metresTime (t) = 3 min 20 seconds

= 200 seconds

Speed (S) =Distance (D)

Time (t) = 1200 metres200 seconds

= 6 m/s11. A bus is moving at 20 metre/sec. How much distance in kilometre

will the bus cover in 25 minutes?Ans. Let the distance be D km.

Speed (S) = 20 m/s = 20 � 60 � 60

1000 km/h

= 72 km/h

Time (T) = 25 min = 2560 h

Distance (D) = Speed (s) × Time (t)

= 72 km/h × 2560 h

= 30 km12. A motor bike is moving with a velocity of 5 metre/second. Its velocity

increases to 25 metre/second over a time span of 10 second.Calculate the acceleration produced by the motor bike.

Ans. Initial velocity (u) = 5 m/sFinal velocity (v) = 25 m/s

Time (t) = 10 seconds


t �

=25 � 5

10 m/s2

= 2 m/s2


13. A car starts from rest, if the engine of the car produces an accelerationof 1.5 metre/second2 for 30 seconds. Calculate final velocity of thecar.

Ans. Let the final velocity be v m/sInitial velocity (u) = 0 Acceleration (a) = 1.5 m/s2



t �

1.5 =v � 030

or, v = 1.5 × 30 m/s= 45 m/s

14. The velocity of a body changes from 2 metre/second to 20 metre/second when the acceleration is 2 metre/sec2. Calculate for howlong the acceleration acts.

Ans. Let the acceleration last for t secondsInitial velocity (u) = 2 m/sFinal velocity (v) = 20 m/sAcceleration (a) = 2 m/s2


t �

2 =20 � 2

t

or, 2 =18t

or, t =182

seconds

or, t = 9 seconds15. A body initially having a velocity “u” is acted upon by an acceleration

of 0.5 m/s2 for 20 s, such that the final velocity of the body is 20


metre/second. Calculate the velocity “u”.Ans. Initial velocity (u) = u

Final velocity (v) = 20 m/sAcceleration (a) = 0.5 m/s2



t �

0.5 =20 �

20u

or, 10 = 20 – uor, u = 10 m/s

16. A stone dropped from the top of a building reaches the ground witha velocity of 49 m/s. If acceleration due to gravity is 9.8 m/s2.Calculate the time for which stone is falling freely.

Ans. Let the stone is falling freely for t seconds.Initial velocity (u) = 0Final velocity (v) = 49 m/s

Acceleration due to gravity (g) = 9.8 m/s2

Using v = u + gt49 = 0 + 9.8 × t

t =499.8 seconds

= 5 seconds17. A stone dropped from a cliff reaches the ground in 1.5 s. If

acceleration due to gravity is 9.8 m/s2. What is the velocity of stonebefore hitting the ground.

Ans. Let the velocity of stone before hitting the ground be v m/sInitial velocity (u) = 0

Time (t) = 1.5 seconds


Acceleration due to gravity (g) = 9.8 m/s2

Using v = u + gtv = 0 + 9.8 × 1.5

or, v = 14.7 m/s18. A body when projected up goes to a height h in time t and then

returns back at the point of projection. Which of the followingstatement is true:(a) the displacement is zero,(b) the average velocity is 2 h/t,(c) the final speed is double the initial speed,(d) the acceleration is zero.

Ans. Since the body returns back to its original position therefore thedisplacement of the body is zero.

19. The value of g remains same at all places on the earth surface. Isthis statement true?

Ans. The given statement is not true because the value of g is maximumat poles and minimum at equator.

20. If a stone and a feather are dropped simultaneously in vacuum fromthe top of a tower, which of the two will reach the ground first.

Ans. Both will reach the ground simultaneously since, acceleration dueto gravity (g = 9.8 m/s2) is same for both a stone and a feather.

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