# UPSC  Physics

51. Ice skating can be used to demonstrate that when ice is under pressure, its

 Melting point is lowered Melting point is raised Melting point remains unchanged Coefficient of friction with metal is reduced

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52. Match the columns:

Names of instruments   The quantities they measure
A. anemometer1. Speed of rotation
B. ammeter2. High temperatures
C. Tachometer3. Wind speed
D. Pyrometer4. electric current
5. Pressure difference

 4 3 1 5 3 4 1 2 3 5 2 1 1 4 5 2

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53. Very small time intervals are accurately measured by the

 Pulsars White dwarfs Atomic clocks Quartz clocks

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54. A ‘black hole’ is a body in space which does not allow any radiation to come out. This property is due to its:

 very small size very large size very high density very low size

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55. The tail of a comet is directed away from the sun because:

 as the comet rotates around the sun, the lighter mass of the comet is pushed away due to the centrifugal force alone as the comet rotates, the lighter mass of the comet is attracted by some stars situated in the direction of its tail the radiation emitted by the sun exerts a radial pressure on the comet throwing its tail away from the sun the tail of the comet always exists in the same orientation

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56. Consider the following statements:
A person in a spaceship located half way between the earth and the sun will notice that the:
1. sky is jet black.
2. stars do not twinkle.
3. temperature outside the spaceship is much higher than that on the surface of the earth.

 3 alone is correct 1 and 2 are correct 1 and 3 are correct 1, 2 and 3 are correct

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57. A stone is tied to a rope and attached to a wooden bar which rotates at constant angular velocity. Suddenly the bar is stopped. The stone gets encircled around the bar. What happens to the angular velocity of the stone.

 Increases Decreases Remains the same First increases and then decreases

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58. The escape velocity from the earth’s surface is about

 30 km/sec 6 km/sec 11.2 km/sec 300 km/sec

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59. If water contracts on freezing, which of the following would happen?

 Icebergs will completely float on the surface of water Ice would become more dense Lakes would freeze from top to bottom Rocks will crack due to freezing or internal water

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60. Two wires have their lengths, diameters and resistivities all in the ratio of 1:2. If the resistance of the thinner wire is 10 ohm, the resistance of the thicker wire is:

 5 ohm 10 ohm 20 ohm 40 ohm

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