99 Percentile Qs Bank for JEE MainPhysicsWaves and Sound
One end of a string is tied to the ceiling of a lift and a load is attached ai the bottom end of the string. When the lift is moving upwards with an acceleration of 2.1 ~ms ⁻² , the speed of the transverse wave at the lower end of the string is 88 ~ms ⁻¹ . If the lift moves downwards with an acceleration of 1.9 ~ms ⁻² , the speed of the transverse wave at the lower end of the string is ( g =10 ~ms ⁻² )
Options
- A88 ~ms ⁻¹
- B102 ~ms ⁻¹
- C119 ~ms ⁻¹
- D72 ~ms ⁻¹
Correct answer
D. 72 ~ms ⁻¹
Step-by-step solution
When lift is moving upwards then frequency n _ u = 1 2 g + a 1 and when moving downwards then frequency n _ d = 1 2 g - a 1 ; wave velocity V = a = a 2 ( n ) 88=2.1 2 ( 1 2 10+2.1 1 ) 1= 12.1 2.1 2.1 88 88 6.9 10⁻³ ~m . When lift is moving downwards then wave speed. V=a =a 2 (n)=1.9 2 1 2 10-1.9 6.9 10⁻³ aligned & =1.9 3.42 10 & V 72 ~m / s . aligned