Questions Related to physics

Multiple choice problems on properties of waves terms and defination used in wave motion oscillation and waves waves physics

Two particles executing SHM of same frequency, meet at x=+A/2, while moving in opposite directions. Phase difference between the particles is 

  1. $\frac{\pi}{6}$
  2. $\frac{\pi}{3}$
  3. $\frac{5\pi}{6}$
  4. $\frac{2\pi}{3}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

At x = A/2, the phase angles are pi/6 and 5pi/6. Since they move in opposite directions, one is at pi/6 (moving away from equilibrium) and the other is at 5pi/6 (moving toward equilibrium). The difference is 5pi/6 - pi/6 = 4pi/6 = 2pi/3.

Multiple choice problems on properties of waves terms and defination used in wave motion oscillation and waves waves physics

Consider the wave represented by $y=\cos(500t-70x)$ where $x$ is in metres and $t$ in seconds. the two nearest points in the same phase have a separation of 

  1. $2\pi/7\ m$
  2. $2\pi/7\ cm$
  3. $20\pi/7\ m$
  4. $20\pi/7\ cm$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

For the same phase, the path difference must be a multiple of the wavelength. Here, k = 70, so 2pi/lambda = 70, lambda = 2pi/70 m = 2pi/70 * 100 cm = 20pi/7 cm.

Multiple choice problems on properties of waves terms and defination used in wave motion oscillation and waves waves physics

Four waves are expressed as
(i) $y _ { 1 } = a _ { 1 } \sin \omega t$                                            (ii) $y _ { 2 } = a _ { 2 } \sin 2 \omega t$
(iii) $y _ { 3 } = a _ { 3 } \cos \omega t$                                         (iv) $y _ { 4 } = a _ { 4 } \sin ( \omega t + \phi )$
The interference is possible between

  1. (i) and (iii)

  2. (i) and (ii)

  3. (ii) and (iv)

  4. Not possible at all

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
For interference frequency should be same.
Ans. (A)
Multiple choice problems on properties of waves terms and defination used in wave motion oscillation and waves waves physics

Equation ${ y } _{ 1 }=0.1sin\left( 100\pi t+\dfrac { \pi  }{ 3 }  \right) $ and ${ y } _{ 2 }=0.1$ cos $\pi t$ The phase difference of the velocity of particle 1, with respect to the velocity of particle 2 is 

  1. $\dfrac { -\pi }{ 6 } $
  2. $\dfrac { \pi }{ 3 }$
  3. $\dfrac { -\pi }{ 3 } $
  4. $\dfrac { \pi }{ 6 } $
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

v1 = dy1/dt = 0.1 * 100pi * cos(100pi*t + pi/3). v2 = dy2/dt = -0.1 * pi * sin(pi*t). This question is garbled regarding the frequencies (100pi vs pi), making a standard phase difference calculation between them invalid.

Multiple choice problems on properties of waves terms and defination used in wave motion oscillation and waves waves physics

Which of the following equations does not represent a progressive wave ?

  1. $y=Asin[\omega (t-\frac { x }{ v } )]$
  2. $y=Asin[ \frac { 2pi }{ \lambda }(vt-x)] $
  3. $y=Asin[2\pi (\frac {t}{T}-\frac { x }{ \lambda } )]$
  4. $y=Asin[2\pi (\frac {t}{T}-\frac { x }{ v } )]$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

A progressive wave must be a function of (vt - x) or (t - x/v). Option D uses (t/T - x/v), which is dimensionally inconsistent if T is period and v is velocity, as t/T is dimensionless but x/v is time.

Multiple choice problems on properties of waves terms and defination used in wave motion oscillation and waves waves physics

A traveling wave is represented by the equation $ y = \frac{1}{10} sin(60 t + 2x) $, where x and y in meters and t is in second . this represents a wave
(1) of frequency $ \frac {30}{\pi} Hz $
(2) of wavelength $ \pi m $
(3)of amplitude 10 cm
(4) moving in the positive x direction
pick out the correct statements from the above.

  1. 1, 2, 4

  2. 1, 3, 4

  3. 1, 2, 3

  4. all

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

y = 0.1 sin(60t + 2x). omega = 60, k = 2. Frequency f = omega/2pi = 60/2pi = 30/pi Hz. Wavelength lambda = 2pi/k = 2pi/2 = pi m. Amplitude = 0.1 m = 10 cm. The wave moves in negative x direction because of the + sign.

Multiple choice problems on properties of waves terms and defination used in wave motion oscillation and waves waves physics

A wave equation which given the displacement along the Y direction is given by $y = 10^{-4} \sin (60t+2x)$ where x and y are in meters and t is time in seconds. This represents a wave 

  1. Traveling with a velocity of 30 m/s in the negative x direction

  2. Of wavelength $\pi $ metre
  3. Of frequency 30/$\pi $hertz
  4. Of amplitude $10^{ -4 }$ metre
Reveal answer Fill a bubble to check yourself
A,B,C,D Correct answer
Multiple choice problems on properties of waves terms and defination used in wave motion oscillation and waves waves physics

For a wave $ y= y _0 sin ( \omega t - kx ) $, for what value of $ \lambda $ , is the maximum particle velocity equal to two times the wave velocity :-

  1. $ \pi y _0 $
  2. $ 2 \pi y _0 $
  3. $ \pi y _0/2 $
  4. $4 \pi y _0 $
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Particle velocity v_p = dy/dt = y0 * omega * cos(omega*t - kx). Max particle velocity = y0 * omega. Wave velocity v_w = omega/k. Given y0 * omega = 2 * (omega/k), so y0 = 2/k. Since k = 2pi/lambda, y0 = 2 / (2pi/lambda) = lambda/pi. Thus, lambda = pi * y0.

Multiple choice problems on properties of waves terms and defination used in wave motion oscillation and waves waves physics

Two small boats are 10 m apart on a lake. Each pops up and down with a period of 4.0  seconds due  to wave motion on the surface of water. What one boat is at its highest point, the other boat is at lowest point. Both boats are always within a single cycle of the waves. The speed of the waves is : 

  1. 2.5 m/s

  2. 5.0 m/s

  3. 14 m/s

  4. 40 m/s

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

If one boat is at crest and other at trough, the distance 10m is half the wavelength (lambda/2). So lambda = 20m. Period T = 4s. Speed v = lambda/T = 20/4 = 5 m/s.