1.      What do you mean by simple machine?

-          The devices which are very simple in structure and make our daily work easy, faster and convenient are known as simple machines. For example: knife, pen, forceps, scissors etc.

2.      How do the simple machines make our works easier?

-          The simple machines make our works easier in the following ways:

i.                    They increase the speed of doing work

ii.                  They transfer the force from one point to another point.

iii.                They multiply the applied force.

iv.                They change the direction of applied force.

3.      Name the type of simple machines.

-          The simple machines are of six types on the basis of their structure which are: Lever, Pulley, Wheel & Axle, Screw, Wedge, Inclined plane.

4.      What is effort?

-          The external force applied to a simple machine to make it work is known as effort.

5.      What is load?

-          The resistance which is overcome by a machine is known as load.

6.      What do you mean by input work?

-          The energy applied to a machine to make it work is known as input work. In another word, input work can also be defined as the work done on the machine by effort is known as input work. Mathematically, Input Work = Effort X Effort Distance

7.      What do you mean by output work?

-          The performance of machine while overcoming load is known as output work. In another word, the work done by the machine is known as output work. Mathematically,             Output work = Load X Load Distance

8.      What do you mean by Mechanical Advantage?

-          Literally, Mechanical Advantage is defined as the capacity of a machine to magnify the effort. Mathematically, it can be defined as the ratio of Load to Effort i.e. MA = Load/Effort. (It doesn’t have any unit, because it is a ratio.)

9.      What do you mean by Velocity Ratio?

-          The Velocity Ratio is defined as the ratio of Effort Distance to the Load Distance. Mathematically, VR = Effort Distance/Load Distance. (It doesn’t have any unit, because it is a ratio.)

10.  Why VR is always greater than MA?

-          It is because the MA is depends on friction while VR depends on the structure of a machine. So, VR is always greater than MA.

11.  A machine has MA = 4, what does it mean?

-          It means that the machine can magnify effort by 4 times.

12.  A machine has VR = 5, what does it mean?

-          It means that the machine has Effort distance 5 times greater than Load distance.

13.  Define Efficiency?

-          Efficiency is defined as the ratio of Output work to the Input work expressed in percentage. Mathematically, Efficiency(ŋ) = (output work/Input work)X100%

-          Similarly, it can also be defined as the ratio of Mechanical Advantage to the Velocity Ratio expressed in Percentage. Mathematically, Efficiency(ŋ) = (MA/VR)X100%

14.  No any simple machine has 100% of efficiency, why?

-          It is because some of the input energy is lost due to the friction. So, no any simple machine has 100% of efficiency.

15.  A machine has 78% of efficiency, what does it mean?

-          It means that 22% of input energy is lost due to friction, only 78% of input work converted into output work.

16.  What do you mean by ideal or perfect machine?

-          The imaginary machines which have 100% of efficiency and do not contain any friction are known as idea or perfect machines.

17.  Differentiate between simple machine and ideal machine.

-          The following are the differences between simple machine and ideal machine:

Simple Machine	Ideal Machine
1.      These bear friction.	1. Theses do not bear any friction.
2.      These never have 100% of efficiency.	2.  These always have 100% of efficiency.
3.      These are real machines.	3. These are imaginary machines.
4.      These are of six types.	4. These do not exist in real life.

18.  What is the working principle of a simple machine?

-          In an ideal machine, input work = output work i.e.                                                             Effort X Effort Distance = Load X Load Distance

19.  What is the working principle of a lever?

-          When a lever is in an equilibrium condition under the action of effort and load, then input work is always equal to output work i.e. Effort X Effort Distance = Load X Load Distance.

20.  What do you mean by lever?

-          Lever is the rigid bar which is capable to rotate about a fixed point (fulcrum) to lift the load is known as lever.

21.  What is fulcrum?

-          The fixed point at which lever is mounted is known as fulcrum.

22.  What is effort distance and load distance?

-          The distance between fulcrum and effort is known as effort distance or effort arm and the distance between load and fulcrum is known as load distance or load arm.

23.  What are the types of lever?

-          On the basis of position of fulcrum, load and effort the lever can be classified into three classes: (i) First Class Lever (ii) Second Class Lever and (iii) Third Class Lever

24.  Define first class lever with suitable examples.

-          The lever in which fulcrum lies between load & effort is known as first class lever. For example: scissors, Nail Puller, Sea Saw etc.

25.  Points to be remembered for first class lever:

-          We can adjust Effort Distance and Load Distance in the first class lever.

-          If ED = LD, then VR = 1, MA=1

-          If ED>LD, then VR.>1, MA>1

-          If ED<LD, then VR<1, MA<1

26.  In metal cutting scissors, cutting edges are made shorter than cloth cutting scissors, why?

-          In metal cutting process more effort is required than cloth cutting. If cutting edges are made shorter, MA will be greater than 1 i.e. effort will be magnified. So in metal cutting scissors, cutting 

edges are made shorter.

27.  Define second class lever.

-          The lever in which load lies between fulcrum and effort. For example: Nut cracker, bottle opener etc. (in second class lever ED>LD, so VR & MA are always greater than 1)

28.  Define third class lever.

-          The lever in which effort lies between fulcrum and load is known as third class lever. For example: forceps, stapler etc. (in third class lever ED<LD, so VR & MA are always less than 1).

29.  A lever of length 1m has been used to lift a load of 600N by applying an effort of 200N. If load is at 20cm from fulcrum, calculate mechanical advantage, velocity ratio and efficiency.

-          Given,        Effort = 200N

Load = 600N

Load Distance = 20cm = 20/100 = 0.2m

Effort Distance = 1-0.2 = 0.8m

MA = ?

VR = ?

Efficiency = ?

                        We know that,             MA = Load/Effort

                                                                   = 600/200

                                                                  = 3

                                                            VR = ED/LD

                                                                  = 0.8/0.2

                                                                  = 4

                                                            Efficiency = (MA/VR)X100%

                                                                            = (3/4)X100%

                                                                             =300/4

                                                                            = 75%

30.  A load of 400N is lifted by an effort of 100N.  If load distance is 20cm, what will be the effort distance?

-          Given         Load = 400N

Effort = 100N

Load Distance = 20cm = 20/100 = 0.2m

Effort Distance = ?

            We know that,             Effort X Effort Distance = Load X Load Distance

                        or, 100 X Effort Distance = 400 X 0.2

                        or, 100 X Effort Distance = 80

                        or, Effort Distance = 80/100

                        or, Effort Distance = 0.8m

31.  A long spanner is used to open a knot, why?

-          It is because a long spanner has greater mechanical advantage than smaller one due to its long effort distance. So a long spanner is used to open a knot.

32.  Differentiate between MA & VR.

-          Following are the differences between MA & VR:

MA	VR
1.      It is the ratio of load to effort	1. It is the ratio of Effort Distance to Load Distance.
2.      It depends on the friction.	2. It depends on the structure of a machine.

33.  Forceps are used in daily life even it has MA is less than 1, why?

-          Because it increases the speed of our daily works and transfers from one point to the another point of machine.

Have a Good Luck and Thanks for Reading.

1.      What do you mean by force?

-          An external agency that changes or tries to change the state of the body is known as force. The SI unit of force is Newton (N). Fundamental unit of force is Kgm/s².

2.      What do you mean by momentum?

-          The product of mass (m) and velocity (v) of a body is known as momentum.

3.      Give mathematical expression of force?

-          Mathematically force can be defined as the rate of change of momentum, F = d(mv)/dt

Since momentum is denoted by P, so, F = dP/dt

4.      What do you mean by 1 N force?

-          As per Newton’s second law of motion, F = ma, where m = mass and a = acceleration. If m = 1kg and a = 1 ms^-2, then F = ma

           = 1kg x 1ms^-2

           = 1kgms^-2

                  = 1N.  Hence, 1N force is defined as the force which can   increase the velocity of a moving body by 1ms^-2 having mass of 1 kg.

5.      What do you mean by rest?

-          The body which is not changing its position with respect to a reference point, then the body is known as in the rest. For example: house, tree etc.

6.      What do you mean by motion?

-          The body which is changing its position with respect to a reference point, then the body is known as in the motion. For example: moving vehicle etc.

7.      Why rest and motion are called relative terms?

-          Rest and motion need comparison with a reference point to explain. So they are called relative terms.

8.      What are the differences between rest and motion?

-          Following are the differences between rest and motion:

Rest	Motion
-          The considering body doesn’t changes its position with respect to the reference point.	-          The considering body changes its position with respect to the reference point.
-          The body has potential energy.	-          The body has kinetic energy.
-          Building, tree etc. are in rest.	-          Moving bus, needle of clock etc. are in motion.

9.      What do you mean by distance?

-          The length of the path travelled by a body between any two points is known as distance. It is a scalar quantity.

10.  What do you mean by displacement?

-          The shortest distance between any two points in a particular direction is known as displacement. It is a vector quantity.

11.  Write down the differences between distance and displacement.

-          Following are the differences between distance and displacement:

Distance	Displacement
-          It is the length of path joining any two points	-          It is shortest distance between any two points in particular direction.
-          It is the scalar quantity.	-          It is the vector quantity.

12.  Can displacement be zero when distance is not zero?

-          Yes. If distance is not raveled in a particular direction, then there is no displacement.

13.  Can distance is zero when displacement is not zero?

-          No. Because displacement is the distance travelled in the particular direction. So, when distance is not zero when displacement is not zero.

14.  Can distance travelled by an object be smaller than magnitude of its displacement?

-          No. Because magnitude of displacement is always less than magnitude of distance.

15.  What do you mean by speed?

-          The distance travelled by a body per unit time is known as speed. It is a scalar quantity. Its unit is m/s. Mathematically, Speed (v) = distance travelled (d)/ time taken (t)

16.  What do you mean by velocity?

-          The distance travelled by a body per unit time in a particular direction is known as velocity. It is a vector quantity. Its unit is m/s.

Mathematically, Velocity (v) = displacement (s)/time taken (t)

 (In another word, velocity is the displacement of a body per unit time.)

17.  What are the differences between speed and velocity?

-          The following are the differences between speed and velocity:

Speed	Velocity
-          It is the distance travelled by a body per unit time.	-          It is the displacement of a body per unit time.
-          It is a scalar quantity.	-          It is a vector quantity.
-          It is always positive or zero but never negative.	-          It may be either positive or zero or negative.

18.  What are the similarities between speed and velocity?

-          The unit m/s.

19.  A body has speed of 10m/s. What does it mean?

-          It means that the body covers the distance of 10 m in each and every second.

20.  A body has velocity of 15m/s. What does it mean?

-          It means that the body covers the distance of 15m in each and every second in a particular direction.

21.  What is average speed?

-          The total distance travelled by a body in a certain time period is known as average speed. Mathematically, Average Speed = Total distance travelled (d)/Total time taken(t)

22.  What is average velocity?

-          The total displacement of a body in a certain time period is known as average velocity. Mathematically, Average Velocity = Total displacement (s)/Total time taken (t)

In another form, Average Velocity = (v₁ + v₂)/2

Similarly, Average Velocity = [initial velocity (u) + final velocity (v)] /2

23.  What is acceleration?

-         The rate of change of velocity is known as acceleration. The SI unit of acceleration is ms^-2        (meter per second square, m/s²). Similarly the negative acceleration is known as retardation. Mathematically, Acceleration (a) = [Final velocity(v) – Initial velocity(u)]/Total time taken(t)

24.  A body has an acceleration of 12ms^-2, what does it mean?

-          It means that the body is increasing its velocity by 12ms^-1 (m/s, meter per second) in each and every second.

25.  A body has an acceleration of 12ms^-2, what does it mean?

-          It means that the body is decreasing its velocity by 12ms^-1 (m/s, meter per second) in each and every second.

26.  When a body is thrown vertically upward, what is velocity at the highest point?

-          It will be zero, because there the body will stop. When a moving body stops, then its final velocity becomes zero.

27.  Can a velocity and acceleration point in opposite direction?

-          Yes, when a body is thrown vertically upward.

28.  Can speed of a body vary with its constant velocity?

-          No, it is not possible. (Because for constant velocity direction and distance per unit time should be constant. For variable speed, distance travelled per unit time and direction is not constant.)

29.  What are equations of motions? (points to be remembered)

-          v = u + at, s = (u+v) x t/2 , s = ut + 1/2at², v² = u² + 2as are equation of motions. These can be explained with five parameters which can be remembered as “suvat” or “utsav”. Similarly, when a body starts from rest the initial velocity becomes 0 and when a body stops the final velocity becomes 0.

30.  Prove v = u + at.

-          u = initial velocity

t = time taken

s = total displacement

a = acceleration

v = final velocity

as per definition, acceleration = (final velocity – Initial velocity)/time taken

                  or, a = (v-u)/t

                  or, at = v – u

                  or, v – u = at

                  or, v = at + u

                  or, v = u + at … … … (i), hence proved.

31.  Prove s = ut + 1/2at².

u = initial velocity

t = time taken

s = total displacement

a = acceleration

v = final velocity

as per definition, acceleration = (final velocity – Initial velocity)/time taken

                  or, a = (v-u)/t

                  or, at = v – u

                  or, v – u = at

                  or, v = at + u

                        or, v = u + at … … … (i)

Similarly, total displacement = average velocity x time taken

            or, s = (u + v) x t/2

            or, s = (u + u + at) x t/2

            or, s = (2u + at) x t/2

            or, s = (2ut + at²)/2

            or, s = 2/2ut + at²/2

            or, s = ut + 1/2at² … … …(ii), hence proved.

32.  Prove v² = u² + 2as.

u = initial velocity

t = time taken

s = total displacement

a = acceleration

v = final velocity

as per definition, acceleration = (final velocity – Initial velocity)/time taken

                        or, a = (v-u)/t

                        or, at = v – u

                        or, v – u = at

                        or, v = at + u

                        or, v = u + at … … … (i)

Squaring on both side of equation (i), we get,

      v² = (u + at)²

or, v² = u² +2uat + a²t²

or, v² = u² + 2a ut + 1/2at² 2a

or, v² = u² + 2a(ut + 1/2at²)

or, v² = u² + 2as … … … (ii)

33.  What do you mean by inertia?

-          The inability of a body to change its position by itself is known as inertia.

34.  What do you mean by inertia of rest?

-          The inability of a body to change its position of rest by itself is known as inertia of rest.

(Dear students the video shows some experiments to show inertia of rest)

35.  What do you mean by inertia of motion?

-          The inability of a body to change its position of motion by itself is known as inertial of motion.

36.  The fruits fall from the tree when branches are shaken, why?

-          It is due to the inertia of rest. When branches are shaken, branches come to the motion but fruit tend to remain in rest and get detached from branches. (Finally due to the gravity, fall down from trees.)

37.  When a bus suddenly starts, passengers fall backwards, why?

-          It is due to the inertia of rest. When bus suddenly starts, the lower part of body comes into the motion but upper part of the body tries to remain in the rest. Hence, passengers of bus fall backwards when bus suddenly starts.

38.  Passengers of a bus fall forward, when a moving bus stops suddenly, why?

-          It is due to the inertia of motion. When a bus stops suddenly, the lower part of the body comes in the rest but upper part of the body tends remain in the motion. So, passengers of a moving bus fall forward when a bus suddenly stops.

39.  A moving fan stops after some time when switched off, why?

-           It is due to the inertia of motion.

40.  Define Newton’s first law of motion.

-          Newton’s first law of motion states that “Everybody continues in its state of rest or in the state of uniform motion in straight line unless an external force is applied.”

41.  Define Newton’s second law of motion.

-          When force is applied on a body it accelerates. So, Newton’s second law of motion states that “Acceleration produced on a body is directly proportional to the force applied and inversely proportional to the mass.”

42.  Define Newton’s third law of motion.

-          Newton’s third law of motion states that “In each and every action there is equal but opposite reaction.”

43.  What do you mean by momentum?

-          The product of mass and velocity of a body is known as momentum.

44.  What is the momentum of a body when it is in rest?

-          The momentum of a body is zero when the body at rest. When the body is in the rest, velocity, v = 0. Therefore, momentum (P) = mass (m) x velocity (v) = m x 0 = 0.

45.  Prove, F = ma.

-          When force is applied on a body, it accelerates. So, as per the definition of Newton’s Second law of motion,  Acceleration produced on a body is

i.                     directly proportional to the force,

a α F … … … (i)

ii.                  inversely proportional to the mass,

a α 1/m … … …(ii)

                   From equation (i) & (ii), we get:

                             a α F/m

                        or, a = k F/m… … … (iii) where, k is the proportionality constant.

            If, a = 1m/s², F  = 1N and m = 1 kg, then k  = 1. Putting k = 1 equation (iii), we get,

                                 a = F/m

                        or, am = F

                        or, F = ma … … … (iv), hence proved.

46.  Define balanced force?

-          If a number of forces acting on a body do not change its state of rest or uniform motion in a straight line, then the forces are called unbalanced forces. eg. in the game of “tug of war.

47.  Define unbalanced force?

-          If a number of forces acting on a body is able to change its state of rest or uniform motion in a straight line, then the forces are called as unbalanced force. eg. when we kick a ball.

48.  What is the acceleration of a person moving with uniform speed?

-          0 m/s²

49.  A car having mass of 1200kg is running with speed of 50m/s. The speed of the car reduced to 20m/s in 20s when driver applied brake seeing a child on the path. Calculate the retardation of the car and force applied by the driver. Also calculate the distance covered.

-          Given, initial velocity (u) = 50m/s

     final velocity (v) = 20m/s

     time taken (t) = 20s

    mass of the car (m) = 1200kg

    acceleration (a) = ?

    force (f) = ?

we know that, a = (v-u)/t

                        = (20-50)/20

                        = -30/20

                        = -1.5 m/s²

Again, as per Newton’s Second Law of Motion, F = ma

                                                                         = 1200 x 1.5

                                                                        = 1800N

Similarly, s = ut + 1/2at²

                     = 50x20 + (-1.5)x20²/2

                = 1000 – 300

               = 700 m

Therefore, the retardation is 1.5m/s², force applied is 1800N and distance covered is 700m

.

50.  A bus is travelling with a velocity of 90km/hr. On seeing school children 20m ahead on the road, the driver applies the brake and the bus stops in a distance of 1.2s. What is its retardation and mention whether the accident happens or not?

-          Given, initial velocity (u) = 90km/hr = 90x1000/60x60 = 90000/3600 = 25m/s

     final velocity (v) = 0 m/s

     time taken (t) = 1.2s

    retardation (a) = ?

    distance covered(s) = ? (dear students, we have to calculate distance covered by vehicle to know whether accident happens or not. If the distance covered by vehicle is more than the distance where the driver sees the children, i.e. 20m, accident happens, otherwise not.)

            We know that, acceleration (a) = (v-u)/t

                                                          = (0-25)/1.2

                                                          = - 2.8m/s²

            Similarly, distance covered (s) = (u+v)xt/2

                                                            = (25+0)x1.2/2

                                                            = (25x1.2)/2

                                                            =30/2

                                                            =15m(Accident doesn’t happen).

51.  A car starts from rest. It maintains an acceleration of 0.5m/s² up to 2 km. Calculate its final velocity and time taken to cover the distance of 1.6km.

-          Given, Initial velocity (u) = 0

        Acceleration (a) = 0.5 m/s²

                Distance (s) = 1.6km = 1.6x1000 = 1600m

            Final velocity (v) = ?

            Time taken (t) = ?

We know that,         v² = u² + 2as

                        or, v = √(0+2x0.5x1600) = 40m/s

again,                     t = (v-u)/a

                        or, t = (40-0)/0.5 = 80s.

52.      What is the relation between inertia and mass?

-          Mass is directly proportional to mass. (inertia α mass)

-GOOD LUCK-