Twinkling of stars is an account of
(a) Large distance of stars and storms in air
(b) Small size of stars
(c) Large size of stars
(d) Large distance of stars and fluctuations in the density of air
18. Most of the sources of energy we use represent stored solar energy. Which of the following is not ultimately derived from sun’s energy
(a) geothermal energy
(b) wind energy
(c) nuclear energy
(d) bio mass
19. A bullet of mass 10 g travelling horizontally with a velocity of 150 m/s strikes a stationary wooden block and comes to rest in 0.03 s. Calculate the magnitude of the force exerted by the wooden block on the bullet.
(a) 50 N (b) 65 N (c) 89.8 N (d) None
20. An artificial satellite is moving in a circular orbit of radius 42250 km. Calculate its speed if it takes 24 hours to revolve around the earth.
(a) 2.01 kms-1
(b) 3.07 kms-1
(c) 1.5 kms-1
(d) 4 kms-1
Solve all questions .
★ Explanation needed ★
DIPTISRIYABISWAL:
2 Q ans is c option
Answers
Answered by
15
Q. Twinkling of stars is an account of ?
Answer: (d) Large distance of stars and fluctuations in the density of air.
When light comes from a star enters the atmosphere of the earth. It undergoes refraction due to the varying optical density of air at various attitudes. The atmosphere is continuously changing due to the optical density of air at different levels in the atmosphere. This continuously changing atmosphere reflects the light from the Stars by different amount from one moment to the next moment.
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Q. 18
Answer: (c) nuclear energy
In nuclear energy the solar energy is not used because in this energy is mainly in the form of heat. Energy is one of the synthetic energy or man-made energy which is produced in the nuclear power plants or laboratories. This energy is produced by the masses of the nuclei of atoms. It is done by the help of nuclear reaction. Nuclear reaction is of two types:
1. Nuclear fusion: It is the process in which two nuclei of light atoms combine to form a heavy and stable nucleus with the liberation of a large amount of energy.
2. Nuclear fission: It is the process in which a heavy atom nuclei splits into two medium sized nucleus with the liberation of an enormous amount of energy.
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Q. 19
Solution:
Given,
For bullet:
Initial Velocity, u = 150 m/s
Final Velocity, v = 0
Mass, m = 10 g = 0.01 kg
Time taken, t = 0.03 s
Let distance of penetration be 's'.
By using the formula of the first equation of the motion.
v = u + at
=> 0 = 150 + a(0.03)
=> a = -5000 m/s^2
Here,
* Negative sign indicates that it is retardation.
By using the formula of the third equation of the motion.
v^2 = u^2 + 2as
0 = 150^2 + 2 × (-5000) × s
=>0 = 22,500 + (-10000) × s
=>10,000 s = 22,500
=> s = 22,500 / 10,000 = 2.25 m
So, s = 2.25 m
Magnitude of the force exerted by the wooden block,
By using the formula of Force.
F = m × a
F = 0.01 × 5000
F = 50 N
Thus, the magnitude of the force exerted by the wooden block on the bullet is 50 N.
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Q. 20
Solution:
Given,
Radius, r = 42,250 km
Time taken, t = 24 hours
Distance covered by the satellite in 24 hours.
By using the formula of distance travelled in terms of circular motion.
S = 2πr
Here, π = 3.14
S = 2 × 3.14 × 42,250
S = 2,65,464.58 km
Now, find out the speed of the satellite.
By using the formula of speed.
V = distance travelled / time taken
V = 2,65,464.58 / 24 × 60 × 60 = 3.07 m/s
Thus, its speed if it takes 24 hours to revolve around the earth is 3.07 m/s
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Answer: (d) Large distance of stars and fluctuations in the density of air.
When light comes from a star enters the atmosphere of the earth. It undergoes refraction due to the varying optical density of air at various attitudes. The atmosphere is continuously changing due to the optical density of air at different levels in the atmosphere. This continuously changing atmosphere reflects the light from the Stars by different amount from one moment to the next moment.
-------------------------------------------------
Q. 18
Answer: (c) nuclear energy
In nuclear energy the solar energy is not used because in this energy is mainly in the form of heat. Energy is one of the synthetic energy or man-made energy which is produced in the nuclear power plants or laboratories. This energy is produced by the masses of the nuclei of atoms. It is done by the help of nuclear reaction. Nuclear reaction is of two types:
1. Nuclear fusion: It is the process in which two nuclei of light atoms combine to form a heavy and stable nucleus with the liberation of a large amount of energy.
2. Nuclear fission: It is the process in which a heavy atom nuclei splits into two medium sized nucleus with the liberation of an enormous amount of energy.
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Q. 19
Solution:
Given,
For bullet:
Initial Velocity, u = 150 m/s
Final Velocity, v = 0
Mass, m = 10 g = 0.01 kg
Time taken, t = 0.03 s
Let distance of penetration be 's'.
By using the formula of the first equation of the motion.
v = u + at
=> 0 = 150 + a(0.03)
=> a = -5000 m/s^2
Here,
* Negative sign indicates that it is retardation.
By using the formula of the third equation of the motion.
v^2 = u^2 + 2as
0 = 150^2 + 2 × (-5000) × s
=>0 = 22,500 + (-10000) × s
=>10,000 s = 22,500
=> s = 22,500 / 10,000 = 2.25 m
So, s = 2.25 m
Magnitude of the force exerted by the wooden block,
By using the formula of Force.
F = m × a
F = 0.01 × 5000
F = 50 N
Thus, the magnitude of the force exerted by the wooden block on the bullet is 50 N.
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Q. 20
Solution:
Given,
Radius, r = 42,250 km
Time taken, t = 24 hours
Distance covered by the satellite in 24 hours.
By using the formula of distance travelled in terms of circular motion.
S = 2πr
Here, π = 3.14
S = 2 × 3.14 × 42,250
S = 2,65,464.58 km
Now, find out the speed of the satellite.
By using the formula of speed.
V = distance travelled / time taken
V = 2,65,464.58 / 24 × 60 × 60 = 3.07 m/s
Thus, its speed if it takes 24 hours to revolve around the earth is 3.07 m/s
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Answered by
0
Answer:- D
In simple terms, twinkling of stars is caused by the passing of light through different layers of a turbulent atmosphere. Most scintillation effects are caused by anomalous refraction caused by small-scale fluctuations in air density usually related to temperature gradients.
The energy required to fuse the lighter nuclei is provided by fission reactions. In this reaction there is no need of sunlight. Therefore nuclear energy is not ultimately derived from Sun's energy. Geothermal energy, wind energy, and bio-mass are all ultimately derived from solar energy.
Initial velocity, u= 150 m/s
Final velocity, v= 0 (since the bullet finally comes to rest)
Time taken to come to rest, t= 0.03 s
According to the first equation of motion, v= u + at
Acceleration of the bullet, a
0 = 150 + (a — 0.03 s)a = -150 / 0.03 = -5000 m/s2
(Negative sign indicates that the velocity of the bullet is decreasing.)
According to the third equation of motion:
v2= u2+ 2as
0 = (150)2+ 2 (-5000)
= 22500 / 10000
= 2.25 m
Hence, the distance of penetration of the bullet into the block is 2.25 m.
From Newton’s second law of motion:
Force, F = Mass * Acceleration
Mass of the bullet, m = 10 g = 0.01 kg
Acceleration of the bullet, a = 5000 m/s2
F = ma = 0.01 * 5000 = 50 N
Hence, the magnitude of the force exerted by the wooden block on the bullet is 50 N.
Distance covered by the satellite in 24 hours
s=2πr
=2×3.14×42250=265464.58 km
Therefore speed of satellite,
v=
time taken
distance travelled
=
24×60×60
265464.58
=3.07 km s
−1
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