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-
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