Science (English Medium) कक्षा ११ - CBSE Question Bank Solutions for Physics

Two electric trains run at the same speed of 72 km h⁻¹ along the same track and in the same direction with separation of 2.4 km between them. The two trains simultaneously sound brief whistles. A person is situated at a perpendicular distance of 500 m from the track and is equidistant from the two trains at the instant of the whistling. If both the whistles were at 500 Hz and the speed of sound in air is 340 m s⁻¹, find the frequencies heard by the person.

A small source of sound oscillates in simple harmonic motion with an amplitude of 17 cm. A detector is placed along the line of motion of the source. The source emits a sound of frequency 800 Hz which travels at a speed of 340 m s⁻¹. If the width of the frequency band detected by the detector is 8 Hz, find the time period of the source.

A boy riding on his bike is going towards east at a speed of 4√2 m s⁻¹. At a certain point he produces a sound pulse of frequency 1650 Hz that travels in air at a speed  of 334 m s⁻¹. A second boy stands on the ground 45° south of east from his. Find the frequency of the pulse as received by the second boy.

A sound source, fixed at the origin, is continuously emitting sound at a frequency of 660 Hz. The sound travels in air at a speed of 330 m s⁻¹. A listener is moving along the lien x= 336 m at a constant speed of 26 m s⁻¹. Find the frequency of the sound as observed by the listener when he is (a) at y = − 140 m, (b) at y = 0 and (c) at y = 140 m.

A train running at 108 km h⁻¹ towards east whistles at a dominant frequency of 500 Hz. Speed of sound in air is 340 m/s. What frequency will a passenger sitting near the open window hear? (b) What frequency will a person standing near the track hear whom the train has just passed? (c) A wind starts blowing towards east at a speed of 36 km h⁻¹. Calculate the frequencies heard by the passenger in the train and by the person standing near the track.

A boy riding on a bicycle going at 12 km h⁻¹ towards a vertical wall whistles at his dog on the ground. If the frequency of the whistle is 1600 Hz and the speed of sound in air is 330 m s⁻¹, find (a) the frequency of the whistle as received by the wall (b) the frequency of the reflected whistle as received by the boy.

A person standing on a road sends a sound signal to the driver of a car going away from him at a speed of 72 km h⁻¹. The signal travelling at 330 m s⁻¹ in air and having a frequency of 1600 Hz gets reflected from the body of the car and returns. Find the frequency of the reflected signal as heard by the person.

A car moves with a speed of 54 km h⁻¹ towards a cliff. The horn of the car emits sound of frequency 400 Hz at a speed of 335 m s⁻¹. (a) Find the wavelength of the sound emitted by the horn in front of the car. (b) Find the wavelength of the wave reflected from the cliff. (c) What frequency does a person sitting in the car hear for the reflected sound wave? (d) How many beats does he hear in 10 seconds between the sound coming directly from the horn and that coming after the reflection?

Figure shows a source of sound moving along X-axis at a speed of 22 m s⁻¹continuously emitting a sound of frequency 2.0 kHz which travels in air at a speed of 330 m s⁻¹. A listener Q stands on the Y-axis at a distance of 330 m from the origin. At t = 0, the sources crosses the origin P. (a) When does the sound emitted from the source at P reach the listener Q? (b) What will be the frequency heard by the listener at this instant? (c) Where will the source be at this instant?

A source of sound emitting a 1200 Hz note travels along a straight line at a speed of 170 m s⁻¹. A detector is placed at a distance 200 m from the line of motion of the source. (a) Find the frequency of sound receive by the detector at the instant when the source gets closest to it. (b) Find the distance between the source and the detector at the instant in detects the frequency 1200 Hz. Velocity of sound in air = 340 m s⁻¹.

A small source of sound S of frequency 500 Hz is attached to the end of a light string and is whirled in a vertical circle of radius 1.6 m. The string just remains tight when the source is at the highest point. (a) An observer is located in the same vertical plane at a large distance and at the same height as the centre of the circle. The speed of sound in air = 330 m s⁻¹ and g = 10 m s⁻². Find the maximum frequency heard by the observer. (b) An observer is situated at a large distance vertically above the centre of the circle. Find the frequency heard by the observer corresponding to the sound emitted by the source when it is at the same height as the centre.

A person stands on a spring balance at the equator. If the speed of earth's rotation is increased by such an amount that the balance reading is half the true weight, what will be the length of the day in this case?

One end of a metal rod is dipped in boiling water and the other is dipped in melting ice.

In summer, a mild wind is often found on the shore of a clam river. This is caused due to

Answer the following question.

Show that its time period is given by, 2π`sqrt((l cos theta)/("g"))` where l is the length of the string, θ is the angle that the string makes with the vertical, and g is the acceleration due to gravity.

Answer the following question.

Define the binding energy of a satellite.

On the basis of dimensions, decide which of the following relations for the displacement of a particle undergoing simple harmonic motion is not correct ______.

1. y = `a sin  (2πt)/T`
2. y = `a sin vt`
3. y = `a/T sin (t/a)`
4. y = `asqrt(2) (sin  (2pit)/T - cos  (2pit)/T)`

If P, Q, R are physical quantities, having different dimensions, which of the following combinations can never be a meaningful quantity?

1. (P – Q)/R
2. PQ – R
3. PQ/R
4. (PR – Q²)/R
5. (R + Q)/P

A function f(θ) is defined as: `f(θ) = 1 - θ + θ^2/(2!) - θ^3/(3!) + θ^4/(4!)` Why is it necessary for q to be a dimensionless quantity?

Why length, mass and time are chosen as base quantities in mechanics?