1
JEE Main 2019 (Online) 10th April Morning Slot
+4
-1
The displacement of a damped harmonic oscillator is given by
x(t ) = e–0.1t cos (10$$\pi$$t + f).
Here t is in seconds. The time taken for its amplitude of vibration to drop to half of its initial value is close to :
A
27 s
B
13 s
C
7 s
D
4 s
2
JEE Main 2019 (Online) 10th April Morning Slot
+4
-1
A stationary source emits sound waves of frequency 500 Hz. Two observers moving along a line passing through the source detect sound to be of frequencies 480 Hz and 530 Hz. Their respective speeds are, in ms–1, (Given speed of sound = 300 m/s)
A
12, 18
B
16, 14
C
12, 16
D
8, 18
3
JEE Main 2019 (Online) 9th April Evening Slot
+4
-1
Two cars A and B are moving away from each other in opposite directions. Both the cars are moving with a speed of 20 ms–1 with respect to the ground. If an observer in car A detects a frequency 2000 Hz of the sound coming from car B, what is the natural frequency of the sound source in car B ?
(speed of sound in air = 340 ms–1) :-
A
2300 Hz
B
2060 Hz
C
2250 Hz
D
2150 Hz
4
JEE Main 2019 (Online) 9th April Evening Slot
+4
-1
A string 2.0 m long and fixed at its ends is driven by a 240 Hz vibrator. The string vibrates in its third harmonic mode. The speed of the wave and its fundamental frequency is :-
A
180m/s, 80 Hz
B
180m/s, 120 Hz
C
320m/s, 120 Hz
D
320m/s, 80 Hz
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