Page 139 - Physics - XI

Q7. When two displacements represented by y = a sin (ωt) and y = b cos (ωt) are superimposed,
2
1
the motion is
a
a. not simple harmonic b. simple harmonic with amplitude
b

c. simple harmonic with amplitude a + b 2 d. simple harmonic with amplitude (ab+ )
2
2
Q8. A particle is executing S.H.M. along a straight line. Its velocities at distances x and x from the
2
1
mean position are V and V , respectively. Its time period is
1 2
x x 2 x x 2 V V 2 2 2
2
2
2
a. 2 1 2 V 2 2 b. 2 2 2 1 2 c. 2 1 2 2 2 d. V V 2
1
V
2
1 2 V V 2 x x 2 x x 2
1
1
1 2
Q9. A particle executes linear simple harmonic motion with an amplitude of 3 cm. When the
particle is at 2 cm from the mean position, the magnitude of its velocity is equal to that of its
acceleration. Then, its time period in seconds is
5 5 4π 2π
a. b. c. d.
π 2π 5 3
Answer key

1. (d), 2. (c), 3. (b), 4. (a), 5. (b), 6. (c), 7. (c), 8. (b), 9. (c)

Assertion-Reason Type Questions

These consist of two statements– Assertion (A) and Reason (R). Answer these questions by selecting
the appropriate option given below:
a. Both A and R are true and R is the correct explanation of A.

b. Both A and R are true and R is not the correct explanation of A.
c. A is true but R is false. d. A is false but R is true.

1. Assertion(A) : A tuning fork of frequency 256 Hz comes into beat with an instrument. The beat
frequency is 10 Hz. Then, the instrument is producing 250 beats/s.
Reason(R) : Beat frequency between two sources of sound is the diff erence of their frequencies.

2. Assertion(A) : Nodes are the points of zero displacement and antinodes are the points of
maximum displacement.

Reason(R) : The distance between two consecutive antinodes is λ.
3. Assertion(A) : A person will hear no sound if he is moving away from the source of sound with
the speed of sound.

Reason(R) : Because the relative motion between the person and source is zero.

Answer key

1. (d), 2. (c), 3. (a)

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