1
JEE Main 2017 (Online) 8th April Morning Slot
+4
-1
Two wires W1 and W2 have the same radius r and respective densities $$\rho$$1 and $$\rho$$2 such that ρ2 = 4$$\rho$$1 . They are joined together at the point O, as shown in the figure. The combination is used as a sonometer wire and kept under tension T. The point O is midway between the two bridges. When a stationary wave is set up in the composite wire, the joint is found to be a node. The ratio of the number of antinodes formed in W1 to W2 is :

A
1 : 1
B
1 : 2
C
1 : 3
D
4 : 1
2
JEE Main 2017 (Offline)
+4
-1
Out of Syllabus
An observer is moving with half the speed of light towards a stationary microwave source emitting waves at frequency 10 GHz. What is the frequency of the microwave measured by the observer? (speed of light = 3 ×108 ms–1)
A
15.3 GHz
B
10.1 GHz
C
12.1 GHz
D
17.3 GHz
3
JEE Main 2016 (Online) 10th April Morning Slot
+4
-1
Out of Syllabus
A toy-car, blowing its horn, is moving with a steady speed of 5 m/s, away from a wall. An observer, towards whom the toy car is moving, is able to hear 5 beats per second. If the velocity of sound in air is 340 m/s, the frequency of the horn of the toy car is close to :
A
680 Hz
B
510 Hz
C
340 Hz
D
170 Hz
4
JEE Main 2016 (Online) 9th April Morning Slot
+4
-1
Out of Syllabus
Two engines pass each other moving in opposite directions with uniform speed of 30 m/s. One of them is blowing a whistle of frequency 540 Hz. Calculate the frequency heard by driver of second engine before they pass each other. Speed of sound is 330 m/sec :
A
450 Hz
B
540 Hz
C
648 Hz
D
270 Hz
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