1
JEE Main 2021 (Online) 24th February Evening Slot
+4
-1
Which of the following equations represents a travelling wave?
A
y = Aexcos($$\omega$$t $$-$$ $$\theta$$)
B
y = Ae$$-$$x2(vt + $$\theta$$)
C
y = A sin (15x $$-$$ 2t)
D
y = A sinx cos$$\omega$$t
2
JEE Main 2021 (Online) 24th February Morning Slot
+4
-1
In the given figure, a mass M is attached to a horizontal spring which is fixed on one side to a rigid support. The spring constant of the spring is k. The mass oscillates on a frictionless surface with time period T and amplitude A. When the mass is in equilibrium position, as shown in the figure, another mass m is gently fixed upon it. The new amplitude of oscillations will be :

A
$$A\sqrt {{M \over {M - m}}}$$
B
$$A\sqrt {{{M - m} \over M}}$$
C
$$A\sqrt {{{M + m} \over M}}$$
D
$$A\sqrt {{M \over {M + m}}}$$
3
JEE Main 2020 (Online) 6th September Morning Slot
+4
-1
A sound source S is moving along a straight track with speed v, and is emitting, sound of frequency v0 (see figure). An observer is standing at a finite distance, at the point O, from the track. The time variation of frequency heard by the observer is best represented by:
(t0 represents the instant when the distance between the source and observer is minimum)
A
B
C
D
4
JEE Main 2020 (Online) 5th September Evening Slot
+4
-1
A driver in a car, approaching a vertical wall notices that the frequency of his car horn, has changed from 440 Hz to 480 Hz, when it gets reflected from the wall. If the speed of sound in air is 345 m/s, then the speed of the car is :
A
36 km/hr
B
54 km/hr
C
24 km/hr
D
18 km/hr
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