What is displacement ?
Answer: C
Displacement is the shortest distance covered in a definite direction.
It is the straight-line vector from start to finish, so it has both magnitude and direction, and can be zero even after a long journey if the body returns to where it began. Distance is the scalar length of the actual path and can only increase.
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Large astronomical telescopes always use as objective a
Answer: C
Large astronomical telescopes use a mirror as the objective.
A big lens can be supported only at its rim, so it sags under its own weight, and it also suffers chromatic aberration. A mirror can be supported across its whole back, is free of chromatic aberration, and needs only one surface figured. The largest refractor ever built is 1 m across; mirrors now exceed 10 m.
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Which of the following uses a Non Renewable Energy Source?
Answer: C
A nuclear power plant uses a non-renewable source.
Uranium ore is a finite mineral resource. Wind, hydroelectric and tidal plants all draw on flows driven continuously by the sun and the moon, and are not depleted by use.
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The cover of a solar cooker is made of glass because
Answer: C
Because it retains the heat inside by the greenhouse effect.
Glass transmits the short-wavelength sunlight that heats the food, but is opaque to the long-wavelength infrared the food then re-radiates. The cover also stops the hot air escaping by convection.
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On a clean glass plate a drop of water spreads to form a thin layer whereas a drop of mercury remains almost spherical because
Answer: D
Because the cohesion of mercury is greater than its adhesion to glass.
A liquid spreads when its adhesion to the surface exceeds its own cohesion, as water does on clean glass. Mercury's cohesive forces are far stronger, so it pulls itself into the shape of least surface area - a sphere - and its meniscus curves the opposite way to water's.
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The intensity of sound at a point is ______ its distance from the source.
Answer: D
Intensity is inversely proportional to the square of the distance.
A point source spreads its power over a spherical wavefront of area \(4\pi r^2\), so \[I = \frac{P}{4\pi r^2}\] Doubling the distance therefore cuts the intensity to a quarter.
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Light from the star, Alpha Centauri, which is nearest to the earth after the sun, reaches the earth in
Answer: C
Its light takes 4.2 years to reach us.
Alpha Centauri is 4.2 light years away, and a light year is precisely the distance light covers in a year. So we see the system as it was more than four years ago - and there is no way to see it as it is now.
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The quality of sound produced by an instrument depends on the
Answer: C
It depends on the number of overtones.
Two instruments sounding the same note produce the same fundamental frequency, but each adds a different set of harmonics in different strengths. That mixture is the timbre, or quality, and it is why a flute and a violin playing middle C are instantly told apart.
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What is the scale used for measuring the intensity of the earthquake?
Answer: C
Earthquake magnitude is measured on the Richter scale.
Devised by Charles Richter in 1935, it is logarithmic: each whole number is a tenfold rise in wave amplitude and about a thirty-twofold rise in energy released. The Mercalli scale, by contrast, records the intensity of the shaking felt at a place rather than the energy at the source.
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A ball is thrown vertically upward from the ground. It crosses a point at the height of 25 m twice at an interval of 4 seconds. The ball was thrown with the velocity of
Answer: C
The ball was thrown at 30 m/s.
The two crossings are symmetric about the highest point, so the ball takes 2 s to go from 25 m up to the apex. Its speed at 25 m is therefore \[v = gt = 9.8\times 2 = 19.6\ \mathrm{m\,s^{-1}}\]
Applying \(v^2 = u^2 - 2gh\) from the ground to that level: \[u^2 = v^2 + 2gh = 384 + 2(9.8)(25) = 874\]
\[u = 29.6 \approx 30\ \mathrm{m\,s^{-1}}\]
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