Question 1 ( 1.0 marks)
In uniform circular motion, the value of which physical quantity changes continuously?
Solution:
In uniform circular motion, the velocity of the moving body changes continuously.
Question 2 ( 1.0 marks)
What would be the acceleration of a body moving with uniform velocity?
Solution:
The acceleration of a body moving with uniform velocity will be zero.
Question 3 ( 1.0 marks)
What do you understand by the distance travelled by a body?
Solution:
The distance travelled by a body is the actual length of the path covered by the body.
Question 4 ( 1.0 marks)
What can be said about the motion of a body if its speed−time graph is a straight line parallel to the time axis?
Solution:
If the speed−time graph of a moving body is a straight line parallel to the time axis, then it can be said that the body is moving with a constant speed, or the body has zero acceleration.
Question 5 ( 1.0 marks)
A ball is rolled on the floor and it stops after some time. Name the unbalanced force that causes the ball to stop.
Solution:
Force of friction is the unbalanced force that causes the ball to stop.
Question 6 ( 1.0 marks)
What is the SI unit of momentum?
Solution:
The SI unit of momentum is kg m s−1.
Question 7 ( 1.0 marks)
What is the value of universal gravitational constant, G, in space?
Solution:
The value of universal gravitational constant, G, in space is 6.7 × 10 −11 Nm2 kg−2.
Question 8 ( 1.0 marks)
What is the acceleration due to gravity on the surface of the moon?
Solution:
The value of acceleration due to gravity on the surface of the moon is 1.62631 m s−2.
Question 9 ( 1.0 marks)
Which wave characteristic determines the loudness of sound?
Solution:
The loudness of sound is determined by the amplitude of the sound wave.
Question 10 ( 1.0 marks)
What are transverse waves?
Solution:
A transverse wave is one in which the particles of the medium vibrate up and down at right angles to the direction in which the wave is moving.
Question 11 ( 1.0 marks)
What is the SI unit of work?
Solution:
The SI unit of work is newton metre (Nm) or joule (J).
Question 12 ( 1.0 marks)
Define power.
Solution:
The rate of doing work is called power.
Question 13 ( 2.0 marks)
A car increases its speed from 10 km/h to 20 km/h in 10 seconds. What is the acceleration of the car?
Solution:
Here,
Initial velocity of the car, u = 10 km/h = 2.77 m/s
Final velocity of the car, v = 20 km/h = 5.55 m/s
Time of acceleration, t = 10 s
From the 1st equation of motion, we get
v = u + at
∴5.55 = 2.77 + a × 10
Therefore, the acceleration of the car is 2.8 m/s2.
Question 14 ( 2.0 marks)
An electric bulb glows when electric current passes through it. Discuss the energy change involved in this process.
Solution:
Electrical energy causes the filament in the bulb to become white-hot. Consequently, the filament gives out light. So, in an electric bulb, electrical energy is first converted into heat energy, and then into light energy.
Question 15 ( 2.0 marks)
Your electricity meter reading of a particular month shows a consumption of 300 units. How much energy is this in joule?
Solution:
1 unit = 1 kWh = 3.6 × 106 J
∴ 300 units = 300 × 3.6 × 106 J
= 1080 × 106 J
= 1.080 × 109 J
Therefore, 300 units meter reading implies 1.080 × 109 J electricity consumption.
Question 16 ( 2.0 marks)
You are travelling in a bus. When the bus suddenly turns, you are thrown to one side. Why?
Solution:
When we travel in a bus, our bodies are set in motion along with the bus, in a straight line. When the bus suddenly turns, the direction of motion gets changed. However, because of inertia, our bodies tend to continue moving along the straight line. Therefore, we are thrown towards the opposite side of the turn.
Question 17 ( 2.0 marks)
Why are road accidents at high speed fatal?
Solution:
If a car travelling at low speed hits an obstruction, then the impact will cause lesser damage to the car as compared to a car travelling at high speed. This will happen because the car moving at high speed will possess greater momentum than the car moving at low speed. Therefore, the force of impact will be greater for the car moving at higher speed, which would in turn be fatal.
Question 18 ( 2.0 marks)
A boy moves 2 km east and then 2 km north. What would be the ratio of the distance travelled by the boy to his displacement?
Solution:
The distance travelled by the boy and his displacement are shown in the given figure.
Total distance covered = AB + BC = 2 + 2 = 4 km
= 2.82 km
Therefore, the ratio of the distance covered by the boy to his displacement is
Question 19 ( 2.0 marks)
The weight of a body is 80 N. What is its mass?
Solution:
Weight of the body = 80 N
We know that
Weight, W = mg
Where,
m = Mass of the body
g = Acceleration due to gravity = 9.8 m/s2
Therefore, 80 = m × 9.8
Or,
Therefore, the mass of the body is 8.16 kg.
Question 20 ( 2.0 marks)
A force of 20 N acts on a body weighing 19.6 N. What is the acceleration produced in the body?
Solution:
Applied force, F = 20 N
Weight of the body = Mass × Acceleration due to gravity
Let the mass of the block be m.
19.6 = m × 9.8
Or,
Therefore, acceleration produced in the body,
Question 21 ( 3.0 marks)
Calculate the force of gravitation due to the earth on a block of mass 10 kg lying on the ground. (Mass of the earth = 6 × 1024 kg; Radius of the earth = 6.4 × 103 km; G = 6.7 × 10−11 Nm2/kg2)
Solution:
The force of gravitation is calculated by using the formula
Here,
G = 6.7 × 10−11 Nm2/kg2
Mass of the earth, m1 = 6 × 1024 kg
Mass of the block, m2 = 10 kg
Radius of the earth = 6.4 × 103 km
= 6.4 × 103 × 1000 m
= 6.4 × 106 m
Now, on putting these values in the above formula, we get
Or,
Or, F = 9.81 × 10 = 98.1 N
Therefore, the force of gravitation due to the earth on the block of mass 10 kg lying on the ground is 98.1 N.
Question 22 ( 3.0 marks)
Mention the medical uses of ultrasound.
Solution:
Medical uses of ultrasound:
(i) It is used for observing the internal parts (which are otherwise difficult to examine) of the human body. This technique is called ultrasonography.
(ii) It is used for monitoring the different stages of development of the foetus inside the womb of a pregnant woman.
(iii) Since ultrasounds are high-frequency or high-energy waves, they can be used for breaking the stones present in gall bladders and kidneys.
Question 23 ( 3.0 marks)
How long will it take for a force of 100 N to stop a mass of 2 kg travelling at a speed of 20 m/s?
Solution:
Here,
F = 100 N
m = 2 kg
u = 20 m/s
v = 0
Since the velocity of the mass is decreasing, a = − 50 m/s2
On applying the first equation of motion, we get
v = u + at
0 = 20 + (−50) t
Or, −20 = −50 t
Or,
Therefore, the mass will stop after 0.4 s.
Question 24 ( 3.0 marks)
Derive the expression for kinetic energy of a moving object.
Solution:
Suppose an object of mass, m is moving with a uniform velocity, u. Let it be displaced through a distance, s when an external force, F acts upon it. Hence, the work done by the force is F × s. Let the final velocity of the object be v,and the acceleration of the body during the change of velocity be a.
From the third equation of motion, we have
v2 − u2 = 2as
We can rewrite the equation as
We know that F = ma
∴ Work done,
Or,
Let us suppose that initially the object was at rest, i.e., u = 0
Then,
Therefore, the kinetic energy possessed by the object of mass, m, moving with uniform velocity, v is
Question 25 ( 5.0 marks)
State Kepler’s three laws of planetary motion.
Solution:
Kepler’s First Law → Each planet moves in an elliptical orbit around the sun, and the sun is located at one of the two foci of the elliptical orbit.
This law means that the orbit of a planet around the sun is an ellipse, and not an exact circle. An elliptical path has two foci, and the sun is at one of the two foci of the elliptical path.
Kepler’s Second Law → Each planet revolves around the sun in such a way that the line joining the planet to the sun sweeps over equal areas in equal intervals of time.
Kepler’s Third Law → The square of the time (T) taken by a planet to move around the sun is directly proportional to the cube of the mean distance (d) of the planet from the sun, i.e., T2 ∝ d3.
Question 26 ( 5.0 marks)
Two bodies having an equal mass move with uniform velocities v and 3v. Find the ratio of their kinetic energy.
Solution:
It is given that the masses of the two bodies are equal. Let the mass of each body be m.
Mass of the first body = m
Velocity of the first body = v
Mass of the second body = m
Velocity of the second body = 3v
To find the ratio of the kinetic energy of the two bodies, we should divide equation (i) by equation (ii).
Thus, we get
 
Therefore, the ratio of the kinetic energy of the two bodies is 1 : 9.
 |