(d) 20,000 Hz - 40,000 Hz
Ans: (a)
58.The angular speed of a whirlwind in a tornado towards the centre [CDS
   2011]
   (a) decreases rapidly
   (b) increases
   (c) remains constant
   (d) slowly becomes zero
Ans: (b)
59.The velocity-time (v-t) graph shown below illustrates- [CDS, 2011]
   (a) uniform acceleration of an object
   (b) uniform retardation of an object
   (c) non-uniform acceleration of an object
   (d) non-uniform retardation of an object
Ans: (b)
60.The velocity of sound in the air (vacuum) is : [RRB Assistt. Driver 2008]
   (a) 330 m/sec
   (b) 220 m/sec
   (c) 110 m/sec
   (d) 232 m/sec
Ans: (a)
61.Sound is a :
   (a) transverse mechanical wave
   (b) longitudinal mechanical wave
   (c) transverse non-mechanical wave
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