Q1. A body travelling with a speed of more than the velocity of sound in air is said to travel with
(a) Supersonic speed
(b) Hypersonic speed
(c) Ultrasonic speed
(d) Infrasonic speed
Q2. An artificial satellite orbiting the earth does not fall down because the earth’s attraction
(a) Is balanced by the attraction of the moon
(b) Vanishes at such distances
(c) Is balanced by the viscous drag produced by the atmosphere
(d) Produces the necessary acceleration of its motion in a curved path
Q3. A long jumper runs before jumping because he
(a) Covers a greater distance
(b) Maintains momentum conservation
(c) Gains energy by running
(d) Gains momentum
Q4. A body is thrown vertically upwards and the falls back on the ground. Its potential energy is maximum
(a) On the ground
(b) At the maximum height
(c) During the return journey
(d) Both on the ground and at the maximum height
Q5. A jet engine works on the principle of conservation of
(a) Linear momentum
(b) Angular momentum
(c) Energy
(d) Mass
Q6. One feels heavier in a lift when the lift
(a) Is going down steadily
(b) Just begins to go up
(c) Is moving up steadily
(d) Descends freely
Q7. The lift of an air plane is based on
(a) Torricelli’s theorem
(b) Bernoulli’s theorem
(c) Law of gravitation
(d) Conservation of linear momentum
Q8. The working principle of a washing machine is
(a) Centrifugation
(b) Dialysis
(c) Reverse osmosis
(d) Diffusion
Q9. The rate of change of momentum of a body equal of the resultant:
(a) Energy
(b) Power
(c) Force
(d) Impulse
Q10. What is the SI unit of intensity of sound?
(a) Decibel
(b) Newton
(c) Hertz
(d) Tesla
Solutions
S1. Ans.(a)
Sol. Supersonic speed is a rate of travel of an object that exceeds the speed of sound. For objects travelling in dry air of a temperature of 20°C at sea level, this speed is approximately 343 m/s.
S2. Ans.(d)
Sol. An artificial satellite orbiting around the Earth does not fall down. This is so because the attraction of earth provides the necessary acceleration for its motion. This acceleration is “constant” in magnitude but “changing in direction”. By the launch rocket, immediately before the satellite is established in the predetermined orbit, the speed given to it is 30,000 km/hr. The speed must be great enough so gravity brings the satellite back be great enough so gravity brings the satellite back to Earth but not so great that the satellite escapes gravity out into space.
S3. Ans.(b)
Sol. A long jumper runs before jumping to maintain momentum. This helps in jumping higher and longer because of inertia of motion gained due to the motion.
S4. Ans.(b)
Sol. We know that
Potential energy = mgh
Hence potential energy is maximum at the maximum height.
S5. Ans.(a)
Sol. A jet engine works on the principle of conservation of linear momentum. In jet engines, a large volume of gases produced by the combustion of fuel is allowed to escape through a jet in the backward direction. Due to the very high speed or velocity, the backward rushing gases have a very large momentum.
S6. Ans.(b)
Sol. One feels heavier in a lift when the lift just begins to go up because our body gains inertia from the position of rest and pushes up against the gravity so here the weight becomes zero and our mass makes us feel heavier.
S7. Ans.(b)
Sol. Bernoulli’s theorem which says that if air speeds up the pressure is lowered. Thus a wing generates lift because the air goes faster over the top creating a region of low pressure, and thus lift.
S8. Ans.(a)
Sol. Washing machine works on the principle of centrifugation. Centrifugation is a process that involves the use of the centrifugal force for the separation of mixtures with a centrifuge, used in industry and in laboratory settings. More-dense components of the mixture migrate away from the axis of the centrifuge, while less-dense components of the mixture migrate towards the exis.
S9. Ans.(c)
Sol. The rate of change of momentum of an object is directly proportional to the resultant force applied and is in the direction of the resultant force.
S10. Ans.(a)
Sol. Decibel(dB) is the SI unit of intensity of sound.
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