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aT WT Niet
PRASHANT KIRAD PRASHANT KIRAD
GRAV.
3
(Options ache se padhna)
MULTIPLE CHOICE Questions (1 Mark)
1. The motion of the moon around the earth is due to:
(a) Centripetal Force
(b) Electrostatic Force
(c) Magnetic Force
(d) Centrifugal Force
2. A body has a mass of 2 kg. When will the mass of the body change?
(a) When the body is taken to the moon.
(b) When the body is dropped from a height.
(c) When the body is being pulled along a smooth surface.
(d) The mass of the body will not change unless it is cut or broken.
3. A girl stands on a box having dimensions 60 cm x 40 cm x 20 cm in different
orientations. In which case will the pressure exerted on the ground be
maximum?
(a) maximum when length and breadth form the base
(b) maximum when breadth and width form the base
(c) maximum when width and length form the base
(d) the same in all the above three cases
4. An object is placed in three liquids of different densities. It floats with 1/4,
1/2, and 3/4 of its volume submerged in liquids with densities di, dz, and ds
respectively. Which is correct?
(a) di> d2>ds
(b) dids
(c) dide (pahle points socho firr likho)
Long Answer Type Questions (5 Marks)
34. . Two objects Also, of masses m1 and m2 having the same size are dropped
simultaneously from heights h1 and h2 respectively. Find out the ratio of time
they would take in reaching the ground. Will this ratio remain the same if:
(A) one of the objects is hollow and the other one is solid and
(B) both of them are hollow, size remaining the same in each case ? give reason.
35.. A man is standing at the top of a 60 m high tower. He throws a ball
vertically upwards with a velocity of 20 m/s. After what time, will the ball pass
him going downwards? How long after its release, will the ball reach the
ground?
36..A ball is permitted to fall from the top of a 200-metre-high tower while
another ball is projected vertically upwards from the round at a speed PRASHANT KIRAD_
of 50 metres per second. Determine when and where the two stones will
meet.
37. (a) State Archimedes’ Principle.
(b) Why does an iron nail sink in water but a ship made of iron float?
(c) A body weighs 500 g in air and 300 g in water. Find the buoyant force
acting on it.
38. (a) Define density and relative density.
(b) Why is the relative density of mercury 13.6?
(c) A solid weighs 100 g in air and 80 g in water. Find its relative density.
39. Two objects of masses 10 kg and 20 kg are placed 2 m apart. Calculate the
gravitational force between them. (Take G = 6.67 x 10-* N-m?/kg’)
40. A body of volume 0.05 m’ is fully immersed in water. Calculate the
buoyant force acting on it. (Density of water = 1000 kg/m’, g = 9.8 m/s”)
41. The value of acceleration due to gravity on the surface of the Moon is
about 1/6th that on Earth. Explain how the weight of an object changes on the
Moon. Also derive the relationship between weight and mass. If a person
weighs 60 N on Earth, what would be his weight on the Moon? Why does his
mass remain unchanged?
42.Define free fall and acceleration due to gravity.
An object is dropped from a height of 78.4 m.
(a) How long will it take to reach the ground?
(b) With what velocity will it strike the ground?
ae paragraph first)
Case Study/Source Based Question
43. Sahil was driving the car at a very high speed to reach the hospital and he
tried to drift the car. But the car slides from a ledge and falls to the ground in
2 seconds due to brake failure. Take acceleration due to gravity, g = 10 m/s?.
(A) What is the speed at which the car hits the ground?
(B) What is the height of the ledge above the ground?
(C) What is more fundamental: mass or weight? PRASHANT KIRAD_
44, There are many forces at work in the universe, as well as many
pushes and pulls. Even if it's just the ground, we're always pushing or pI
something. However, it turns out that there are just four fundamental forces i in
Physics, from which everything else is derived: The strong. weak,
electromagnetic, and gravitational forces. The gravitational force is a force that
attracts all mass-bearing objects. The gravitational forcee is referred to as
attractive because it always strives to pull masses together rather than pushing
them apart. In reality, everything in the cosmos, including you, is tugging on
every other object! This is referred to as Newton's Universal Law of Gravitation.
(A) On the surface of the Earth, a body of mass 1kg is attracted by the Earth with
a force equal to:
(a)1N
(b) 98N
(c) 9.8.N
(d) 10 N.
(B) What is the mass of an object whose weight is 98 N?
(a) 10 kg
(b) 1kg
(c)1g
(d)10g
(C) The gravitational force causes:
(a) Tides
(b) Motion of moon
(c) None of them
(d) Both (a) and (b)
(D) Assertion: The Earth and the ball pattract each other with an equal
gravitational force. Reason: The Earth moves towards the ball.
(a) Both (A) and (R) are true, and (R) is the correct explanation of (A).
(b) Both (A) and R are true, and (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.
(E) The SI unit of upthrust is:
(a) Newton
(b) m/s
(c) Pascal
(d) m/s? PRASHANT KIRAD
PK Special [KBC] ae
45. Why does the value of ‘g’ decrease as we go above the Earth's surface or
inside the Earth? Explain
46. Explain why a person feels lighter while swimming. Name the force
responsible for this.
47. Why do objects weigh less on the Moon than on Earth? Give numerical
comparison.
48. Calculate the gravitational force between two masses of 5 kg and 8 kg
placed 0.6 m apart.
(Take G = 6.67 x 10-* N-m?/kg?)
49. A2 kg object is dropped from a height of 20 m. Calculate:
(a) Potential energy at the top
(b) Speed just before hitting the ground
(g= 9.8 m/s?) PRASHANT KIRAD
MULTIPLE CHOICE TYPE QUESTIONS
LA
2.D
3.C
4A
5.c
6.D
7.
8.B
9A
10.¢
11.B
12.A
13.¢
14.D
15.B
ASSERTION AND REASONS TYPE QUESTIONS:
16. (a)
17. (a)
18. (a)
19. (a)
20. (a)
SHORT ANSWER TYPE QUESTIONS
21. Both stones will reach the ground at the same time.
Reason:
The vertical motion of both stones is influenced only by the acceleration
due to gravity (g).
The stone thrown horizontally has an extra horizontal velocity, but this
does not affect its vertical fall.
The time taken to fall from a certain height depends only on vertical
motion and initial vertical velocity (which is zero for both).
Thus, since both are falling under gravity from the same height and have zero
initial vertical velocity, they will take the same time to reach the ground PRASHANT KIRAD
22. The buoyant force always acts in the upward direction, opposite to the
direction of gravity.
* When an object is immersed in a fluid, the pressure at the bottom of the
object is greater than at the top due to fluid depth.
* This pressure difference causes a net upward force called the buoyant force.
* Hence, it acts vertically upward through the center of buoyancy.
23. Given:
Height (h) = 20 m
Initial velocity (u) = 0 (free fall)
Acceleration due to gravity (g) = 9.8 m/s?
We use the formula:
v=u?+2gh
v?=0+2%9.8*20 = 392
v= V¥392 = 19.8 m/s (approx.)
24. Astronauts feel weightless in space because they are in a state of free fall
inside their spacecraft.
Both the spacecraft and astronauts fall toward the Earth due to gravity with the
same acceleration.
» As there is no normal reaction force acting on them, they experience a
condition of zero apparent weight.
* This sensation is called weightlessness, though gravitational force still acts
onthem.
25. Standing will exert more pressure because pressure = force / area.
When standing, the area of contact is less, so pressure is more.
26. Because the acceleration due to gravity (g) on the Moon is 1/6th that on
Earth.
Since weight = mass * g, the weight becomes 1/6th.
27. The fraction of volume submerged = density of block / density of water
Given:
Volume submerged = 3/4
So,
Density of block = 3/4 x 1000 = 750 kg/m? PRASHANT KIRAD_
28. (A) When a body is thrown vertically upwards, its velocity decreases due to
gravity.
‘At the maximum height, the velocity becomes zero before the body starts falling
back down.
(B) Mass is more fundamental than weight.
* Mass is a scalar quantity and remains constant everywhere.
* Weight = mass x gravity (W = mg) and depends on gravity, which varies with
location.
29. (A) No, the gravitational force between two objects does not depend on the
medium between them.
It depends only on their masses and distance between them, as per Newton’s law of
gravitation.
(B) The gravitational force becomes large when:
* The masses involved are very large (like Earth and Moon).
* The distance between the objects is very small (since force is inversely
proportional to square of distance).
30. (A) Initial water level = 30 mL, Final level = 42 mL
Volume of copper piece = 42 - 30 = 12 cm*
(B) Mass = 120 g, Volume = 12 cm®
Density = Mass / Volume = 120 / 12 = 10 g/cm*
31. Mass = 50 g, Volume = 20 cm*
Density of substance = 50 / 20 = 2.5 g/cm*
Density of water = 1 g/cm?
Since the substance is denser than water, it will sink in water.
32. The acceleration due to gravity (g) changes with both depth and altitude:
* As we go deeper into the Earth, value of g decreases because the effective mass
attracting the object becomes less.
As we go to a higher altitude, g also decreases because the distance from Earth’s
center increases, reducing gravitational pull.
33. We know:
go density of Earth (g = 4/3 1 « G « R density)
If the density is halved but radius remains the same, then:
New g=%* original g
So, acceleration due to gravity will become half its o1 PRASHANT KIRAD_
34. The time taken by an object falling freely from height h is given by:
t=v(2h/g)
So, for two objects dropped from heights h; and hz, their time of fall will be:
(2ha/ g)
(2he/ 8)
Therefore, the ratio of time taken:
ti / te=v(hi/ he)
This ratio depends only on the heights from which they are dropped, not on
mass or size.
(A) One object is hollow, other solid:
In vacuum, both fall with the same acceleration due to gravity. So, the time
taken depends only on height — ratio remains same.
In air, a hollow object may experience more air resistance, so it may fall slightly
slower. Hence, the ratio may vary slightly.
(B) Both are hollow, same size:
Since both are affected equally by air resistance, the time taken depends only
on their heights. The ratio remains same. t: / tz = V(hi / he)
Ratio remains the same in vacuum. In air, it can vary if air resistance differs.
35. iven:
+ Initial velocity, u = 20 m/s
* Acceleration due to gravity, g = 9.8 m/s?
¢ Height of tower = 60m
(A) Time to reach back to same height (where man is standing):
At maximum height, final velocity v = 0
Using the equation:
veu-gt
0=20-9.8t
=>t=20/9.8=2.04s
‘So, the ball will pass the man after 2.04 seconds while coming down.
(B) Time to reach the ground:
First, find maximum height reached by the ball: PRASHANT KIRAD
35. h =u? / (2g) = 207 / (2 « 9.8) = 400 / 19.6 = 20.41m
Total height from maximum point to ground:
H=60+20.41=80.41m
Now, time taken to fall from max height to ground:
= (1/2)gt? > t= v(2s/g)
t=v(2 x 80.41 / 9.8) = (16.41) = 4.05 s
Total time = time to reach top + time to fall = 2.04 + 4.05 = 6.09 seconds
36. Let the two balls meet after t seconds.
Let:
* Height of the tower =200m
For Ball A (falling from the top):
Initial velocity, u: = 0 m/s,
Distance covered in time t = s: = %-g-t?
For Ball B (rising from ground):
Initial velocity, uz = 50 m/s,
* Distance covered = sz = urt - ¥eg-t?
They meet when the sum of distances covered by both = total height of the tower:
So,
Si +S2=200
> Yegt? + (50-t - %gt?) = 200
=> 50-+=200
=> t=4 seconds
We can use the distance travelled by the second ball (ri
s=ut—Yegt?
=50%4-%%9.8 x 4?
=200-0.5*9.8x16
=200-78.4
=121.6m
* The two balls will meet after 4 seconds
* They will meet at a height of 121.6 metres above the ground
37. Let the height of the tower = 200 m
Ball A is dropped from the top (initial velocity us = 0)
Ball B is projected upwards from the ground with u2 = 50 m/s
Let they meet after t seconds
* For Ball A (falling):
© srs Megtt=%ex9.8xt? PRASHANT KIRAD_
O-t — ex 9.8 x t?
$1 +S2= 200
> (egt?) + (50-t — %-g+t?) = 200
=> 50-t=200
=> t=4 seconds
Now, distance from ground =50-t- %4-9.8-t?
=50*4-%x9.8x16
=200 - 78.4
=121.6m
The balls meet after 4 seconds at a height of 121.6 m above the ground.
38. (a) Archimedes’ Principle:
When a body is immersed in a flui experiences an upward force (buoyant
force) equal to the weight of the fluid displaced by it.
(b) An iron nail sinks because it displaces less water than its own weight, so the
buoyant force is less.
Aship made of iron floats because it displaces a large volume of water, making
the buoyant force equal to its weight.
(c)
Buoyant Force = Weight in air - Weight in water
=500 g- 300 g=200 g=2N
(1g=0.01N)
39. Formula:
F=G@mim:/
Given:
m; = 10 kg, mz = 20 kg, r= 2m
G = 6.67 x 10-* N-m?/kg?
F = (6.67 x 10-* x 10 x 20) / 2?
= (1334 x10-¥) /4
=3.335*10°N
40. Formula:
F_b=p-V-g PRASHANT KIRAD_
Given: p = 1000 kg/m‘, V = 0.05 m’*, g = 9.8 m/s?
F_b=1000 = 0.05*9.8
=490N
41. Weight = mass * acceleration due to gravity
On Moon, g_moon = (1/6)-g_earth
W_moon = m « g/6 = W_earth / 6
If W_earth = 60 N, then:
W_moon = 60/6=10N
Mass remains unchanged because it is independent of gravity
42. Free fall: Motion of a body under gravitational force alone is called free fall.
Acceleration due to gravity (g): Acceleration of a body in free fall. On Earth, g =
9.8 m/s?
Given: h = 78.4 m, g = 9.8 m/s?
(a)
t=v(2-h/g)
=v(2* 78.4 / 9.8)
=v16=4s
(b)
v=gt=9.8x4=39.2 m/s
CASE STUDY/SOURCE BASED QUESTION:
43. A. We use the formula:
veutgt
where:
+ u=0 m/s (initial velocity, as the car starts falling from rest),
* g=10 m/s? (acceleration due to gravity),
+ ts2s
So,
v=0+10*2=20 m/s
B. Use the formula:
s=ut+ (1/2)-g-t?
Here, PRASHANT KIRAD_
* u=Omis,
* g=10 m/s’,
*ts2s
So,
S$=0+¥%x10x(2)?=5*x4=20m
C. Mass is a fundamental quantity because it is constant everywhere in the universe
and does not change with gravity.
Weight depends on gravitational force and varies from place to place (e.g.,on Moon
or Earth).
Mass is more fundamental than weight because it is a constant physical quantity,
whereas weight depends on gravity.
PK Special [KBC]
45. The value of ‘g’ (acceleration due to gravity) decreases as we go above the Earth’s
‘surface or inside the Earth because:
* Above Earth’s Surface: As height increases, the distance from the center of the
Earth increases. Since g 1/R®, the gravitational pull weakens with distance.
* Inside the Earth: As we go deeper, the mass of the Earth above us no longer
contributes to gravity, so the effective mass attracting the object decreases.
Hence, g decreases.
46. A person feels lighter while swimming because of the buoyant force
exerted by water.
This force acts upward and opposes the weight of the body, reducing the net
downward force, making the person feel lighter.
Force responsible: Buoyant force (Upthrust)
47. On the Moon, objects weigh less because the gravitational force is weaker.
g_moon = 1/6 x g_earth
If a body weighs 60 N on Earth: PRASHANT KIRAD_
Weight on Moon=60+6=10N
Hence, objects weigh 1/6th on the Moon compared to Earth.
48. Given:
kg, m2 = 8 kg, r= 0.6 m,
G = 6.67 x 10-* N-m?/kg?
Gravitational Force (F)
F=G~x(mi* m2) / 1?
F = (6.67 x 10-) x (5 * 8) / (0.6)?
F = (6.67 x 10-* x 40) / 0.36
F=2.96x10°N
Answer: 2.96 x 10° N
49. Given:
m=2kg, h=20 m, g = 9.8 m/s?
(a) Potential Energy (PE):
PE =mgh =2* 9.8 x 20 = 392J
(b) Speed just before hitting ground:
Using: v? = 2gh
v?=2* 9.8 x20 = 392
Vv =¥392 = 19.8 m/s (approx) PRASHANT KIRAD_
49. Voluntary muscles (also called skeletal or striated muscles) are long, cylindrical,
multinucleated, and striated. These muscles are arranged in bundles and are
connected to bones. Their structure allows for quick and powerful contraction,
which is under conscious control. This helps in activities like walking, writing, and
lifting objects.
Involuntary muscles, such as smooth muscles and cardiac muscles, are spindle-
shaped (smooth) or branched (cardiac) and have one nucleus. These muscles
contract slowly and rhythmically without conscious control. They are found in
internal organs like the stomach, intestines (smooth), and the heart (cardiac).
Comparison:
Voluntary muscles + Rapid, controlled movement (due to striated, bundled
structure)
Involuntary muscles + Slow, automatic functions (due to smooth or branched
structure)
Thus, the structure of muscle fibers is directly related to their function in body
movement and control.
50. Xylem is a complex permanent tissue in plants responsible for the transport of
water and minerals from the roots to other parts of the plant. It also provides
mechanical strength.
Xylem Components:
1 Tracheids - Long, narrow dead cells with thick lignified walls and tapering ends.
2.Vessels — Wider, tube-like dead cells joined end-to-end to form long pipelines.
3.Xylem Fibres - Dead, thick-walled supportive cells.
4.Xylem Parenchyma - Living cells that store food and help in lateral conduction.
Function:
* Conducts water and mineral salts from roots to shoots.
* Provides structural support to the plant.
Importance of Lignin Deposition:
Lignin is a complex organic substance that is deposited in the cell walls of tracheids
and vessels. It makes the walls thick, rigid, and waterproof, which prevents them
from collapsing under the pressure of water transport. It also helps maintain the
integrity and strength of xylem tissues.
51. Neuron is the basic structural and functional unit of the nervous system. It is
specialised to transmit nerve impulses quickly and efficiently across long distances.
Structure of a Neuron:
5. Dendrites — Short, branched projections that receive signals.
6.Cell Body (Cyton) - Contains the nucleus and cytoplasm; integrates signals. PRASHANT KIRAD_
1.Axon - A long, tubular extension that carries impulses away from the cell body.
2.Axon Terminals - Pass signals to other neurons or effectors.
3.Myelin Sheath — Fatty layer covering the axon, increases impulse speed.
Functiot
Neurons receive, process, and transmit electrical impulses to other neurons,
muscles, or glands.
Difference from Muscle Tissues:
* Neurons transmit electrical signals; muscle tissues contract to produce
movement.
* Neurons have branched and long extensions (axon, dendrites); muscle cells are
elongated and fibrous.
* Neuron signals are electrical and chemical, while muscles work via mechanical
contraction.
Axon terminals
Soma
(cell body)
52. Desert plants (xerophytes) are adapted to conserve water in harsh, dry
environments. They have:
* Thick cuticle: A waxy layer on the epidermis that prevents excessive water loss
through evaporation.
* Sunken stomata: Stomata are located in pits to trap moisture and reduce
transpiration.
Tissues Involve
* Epidermal tissue (protective tissue) forms the outer covering with cuticle.
* Parenchyma tissue in leaves stores water and may assist in photosynthesis.
These adaptations help desert plants survive in conditions where water is scarce.
