Home Courses Contact About




6. (JEE Main 2021 (Online) 31st August Morning Shift)

A wire having a linear mass density 9.0 × 10 4 kg/m is stretched between two rigid supports with a tension of 900 N. The wire resonates at a frequency of 500 Hz. The next higher frequency at which the same wire resonates is 550 Hz. The length of the wire is ____________ m.

Correct Answer is 10

μ = 9.0 × 10 4 k g m

T = 900 N

V = T μ = 900 9 × 10 4 = 1000 m/s

f1 = 500 Hz

f = 550

n V 2 l = 500 .... (i)

( n + 1 ) V 2 l = 500 .... (ii)

(ii) (i) V 2 l = 50

l = 1000 2 × 50 = 10

7. (JEE Main 2021 (Online) 26th February Morning Shift)

The mass per unit length of a uniform wire is 0.135 g/cm. A transverse wave of the form y = 0.21 sin (x + 30t) is produced in it, where x is in meter and t is in second. Then, the expected value of tension in the wire is x × 10 2 N. Value of x is _________. (Round off to the nearest integer)

Correct Answer is 1215

μ = 0.135 gm/cm

μ = 0.135 × 10 3 10 2 k g m

y = 0.21 sin (x + 30t)

v = ω K = 30 1 = 30 m/s

v = T μ

T = v2 × μ

T = (30)2 × 0.135 × 10 1

T = 900 × 0.135 × 10 1

T = 12.15 N

T = 1215 × 10 2 N

x = 1215

8. (JEE Main 2021 (Online) 25th February Evening Shift)

The percentage increase in the speed of transverse waves produced in a stretched string if the tension is increased by 4%, will be __________%.

Correct Answer is 2

Speed of transverse wave is

V = T μ

ln V = 1 2 ln T 1 2 ln μ

Δ V V = 1 2 Δ T T

= 1 2 × 4

Δ V V = 2 %

9. (JEE Main 2020 (Online) 3rd September Morning Slot)

A uniform thin rope of length 12 m and mass 6 kg hangs vertically from a rigid support and a block of mass 2 kg is attached to its free end. A transverse short wavetrain of wavelength 6 cm is produced at the lower end of the rope. What is the wavelength of the wavetrain (in cm) when it reaches the top of the rope ?

A. 12

B. 3

C. 9

D. 6

Correct Answer is Option (A)

JEE Main 2020 (Online) 3rd September Morning Slot Physics - Waves Question 60 English Explanation

T1 = 2g

T2 = 8g

V = T μ

V T

Also V = f λ

V1 = f1 λ 1

and V2 = f2 λ 2

We know frequency of sources are same.

f1 = f2

So T 1 T 2 = λ 1 λ 2

2 g 8 g = 6 λ 2

λ 2 = 12 cm

10. (JEE Main 2020 (Online) 2nd September Morning Slot)

Two identical strings X and Z made of same material have tension TX and TZ in them. If their fundamental frequencies are 450 Hz and 300 Hz, respectively, then the ratio TX/TZ is :

A. 2.25

B. 0.44

C. 1.25

D.

Correct Answer is Option (A)

f = 1 2 l T μ

For identical string l and μ will be same

f T

450 300 = T x T y

T x T y = 9 4 = 2.25