Kerala Syllabus Class 9 Physics Model Question Paper Set 3 English Medium

Teachers recommend solving Kerala Syllabus 9th Standard Physics Question Paper Set 3 to improve time management during exams.

Kerala Syllabus Std 9 Physics Model Question Paper Set 3 English Medium

Time: 1½ Hours
Max Score: 40 Marks

Instructions

• First 15 minutes is given as cool off time. This time is to be spent for reading and understanding the questions.
• Answer the questions according to the directions.
• Score and time to be considered while answering.

I. Answer any three questions from 1 to 4. (1 score each) (3 × 1 = 3)

Question 1.
Which phenomenon of light is used in optical fibres that are used for communication?
Answer:
Total internal reflection

Question 2.
Identify the relation between the first pair and complete the second
Momentum: m × v; Impulse: _____
Answer:
Ft

Question 3.
If a car starts from rest, what is its initial velocity (U)?
Answer:
0

Question 4.
Observe the instruments A and B shown in the figure.

Among these which is used to measure mass? (Instrument A, Instrument B)
Answer:
Instrument A

II. Answer any seven questions from 5 to 13. (2 score each) (7 × 2 = 14)

Question 5.
Match the following.

Answer:

Question 6.
A car of 1000 kg moves with a velocity of 20 m/s. On applying brakes, it comes to rest in 5 s.
a) What is its initial momentum?
b) What is its final momentum?
Answer:
a) Initial momentum = mu = 1000 × 20
= 20000 kg m/s

b) Final momentum = mv = 1000 × 0
= 0 m/s

Question 7.
The refractive index of diamond is 2.42. What do you mean by this? Calculate the speed of light through diamond.
Answer:
Light travels through the air with a velocity 2.42 times the velocity of light through a diamond.
v = \(\frac { c }{ n }\) = \(\frac{3 \times 10^n}{2.42}\) = 1.24 × 10⁸ m/s

Question 8.
Write an activity to prove inertia of rest.
Answer:
Make a pile of coins on a table. Strike off the lowest coin with a knife quickly. Only that particular coin is thrown off, and the others remain in the previous manner. This is due to the tendency of coins to remain in their state of rest.

Question 9.
A car starts from rest and covers 20 m in 2s. Calculate the acceleration of the car.
Answer:
u = 0
s = 20 m
t = 2 s
s = ut + 1/2 at²
20 = 0 × 4 + 1/2 × a × 2²
20 = 2a
a = 10 m/s²

Question 10.
The mass of a body is 10 kg. Find the weight of the body if it is placed on the surface of ‘Jupiter’. (Value of g at Jupiter, g = 23.1 m/s²)
Answer:
Weight = mg
Weight = 10 × 23.1 = 231 N

Question 11.
When we place a glass slab on the letters in a textbook, the letters appear raised. What may be the reason?
Answer:
The ray of light coming from the letters undergoes refraction through the glass slab and reaches the eye. So the letters appear raised.

Question 12.
a) The weight of a freely falling body is zero. Why?
b) What do you mean by free fall?
Answer:
a) The weight of a freely falling body is zero because the entire force of gravity is used to provide acceleration to the body.
b) If an object is allowed to fall freely from a height, it will fall to the ground only under the gravitational force of the Earth. Such a motion is called free fall.

Question 13.
The velocity-time graph of a moving car is given below.

a) Find the acceleration of the car from A to B.
b) Which part of this graph represents the deceleration of the car?
Answer:
a) 0 (From A to B the car has uniform velocity, so no acceleration takes place)
b) BC

III. Answer any five questions from 14 to 19. (3 score each) (5 × 3 = 15)

Question 14.
A ray of light travels from air to a glass slab is depicted below. Observe the figure and answer the questions.

a) Find out the incident ray.
b) Find out the refracted ray.
c) What is the angle of incidence?
d) What is the angle of refraction?
e) What happens when a ray of light obliquely travels from air to a glass slab?
f) Name this phenomenon of light.
Answer:
a) PQ
b) QR
c) 30°
d) 19°
e) It bend towards the normal (refraction takes place)
f) Refraction

Question 15.
An object starting from rest travels with a uniform acceleration of 8 m/s². Calculate the velocity and distance travelled after 40 s.
Answer:
u = 0
a = 8 m/s²
t = 40 s
v = u + at = 0 + 8 × 40 = 320 m/s
s = ut + 1/2 at²
= 0 × 40 + 1/2 × 8 × 40²
= 6400 m

Question 16.
Give reasons for the following.
a) Accidents that happen to passengers who do not wear seat belts are more fatal.
b) At the time of catching a cricket ball, the time of catching is extended by moving the hand backwards with the ball.
c) Action and reaction do not cancel each other.
Answer:
a) It is due to inertia of motion. In moving vehicle, the passengers are also in the state of motion. When the vehicle is suddenly stopped the passengers have the tendency to move forward and hit on the body of vehicle that causes accident more fatal if they do not wear seat belt.

b) It is to reduce impulsive force, thereby reducing the momentum and impact on our hand.

c) Action and reaction are equal and opposite but they never cancel each other because they act on different objects.

Question 17.
A ball thrown vertically upward reached a maximum height of 20 m.
a) What was the velocity of the stone at the instant of throwing up?
b) How much time did the ball take to reach the height of 20 m ?
Answer:
a) v² = u² + 2as
u² = v² – 2as
u² = 0² – 2× -10 × 20
u² = 400
u = 20 m/s

b) v = u + at
t = \(\frac { v-u }{ a }\) = \(\frac { 0-20 }{ -10 }\) = 2s

Question 18.
State true or false.
a) The value of G is constant everywhere in the universe.
b) The value of g is constant everywhere in the universe.
c) The weight of an object is constant everywhere in the universe.
Answer:
a) True
b) False
c) False

Question 19.
The refractive index of different mediums is given in the table.

Medium	Refractive index
Crown glass	1.52
Glycerine	1.47
Sunflower oil	1.47
Water	1.33
Flint glass	1.62

a) In which medium does light travel with maximum speed?
b) Will a ray of light entering obliquely from glycerine to sunflower oil deviate? Explain the reason.
c) Light is transmitted from glass to each medium listed in the table above. If the light is incident at an angle of 30°, which medium will have the largest angle of refraction? Why?
Answer:
a) In water

b) No. As the speed of light is the same in both these mediums (as the refractive index of both mediums is the same), light does not undergo refraction.

c) In water. Among these, water has the least refractive index.

IV. Answer any two questions from 20 to 22. (4 score each) (2 × 4 = 8)

Question 20.
Justify the statements.
a) While bow fishing, one should aim at a point below the perceived position of the fish.
b) The bottom of the aquarium is seen above the surface of the water.
Answer:
a) When the reflected light coming from the fish enters from an optically denser medium (here water) to a rarer medium(air), it deviates away from the normal at the surface of separation. This refracted light appears to come from a position just above the actual position. This is why it is advised to aim at a point below the perceived position of the fish.

b) The light coming from the bottom of the aquarium undergoes internal reflection at the surface of water. Hence, the bottom is seen above the surface of water. The distance from the surface of water to the bottom of the aquarium is the same as the – distance from the surface to the image caused by total internal reflection.

Question 21.
Observe the given graphs.

a) Which among the graphs represents the body at rest?
b) The other graph represents _____ (uniform acceleration / uniform velocity)
c) What is the velocity of the body shown in graph (i)?
d) How much will be the acceleration for the body represented by graph (ii)?
Answer:
a) graph(1)
b) uniform velocity
c) Zero (because the body is at rest)
d) Zero (because the body is in uniform velocity, it has no acceleration)

Question 22.
A body of mass 10 kg is taken to different parts of the Earth.
a) What is its mass at the centre of the earth?
b) Where does it have maximum weight?
c) At which part on the surface of the earth is the weight minimum?
d) In your opinion, what is the cause of this difference in weight?
Answer:
a) 10 kg
b) At poles
c) At equatorial places
d) As the radius of the earth (R) changes, the value of g\(\left(g=\frac{G M}{R^2}\right)\) changes and, weight (w = mg) changes.