SHM & Waves

Physics 152

How does the complex number Aeiωt move in the complex plane as time t steadily increases?

1. It moves exponentially further from the origin.

2. It goes around a circle at an increasing speed.

3. It goes around in a circle at a steady speed.

A mass m is suspended on a spring which exerts a force F = -kx when the mass is x from equilibrium, and oscillates with period 1 second. A mass 4m on the same spring would oscillate with period:

1. 0.25 seconds

2. 0.5 seconds

3. 2 seconds

4. 4 seconds

If z(t) = Ae it, dz/dt = iAe it. In the complex plane, the complex number dz/dt is:

1. In the same direction as the number z

2. In a direction perpendicular to that of z.

A pendulum subject to a very large drag force –bv is pulled to one side, and let go. The time taken to swing back to rest is mainly determined by:

1. m/b (has dimension of time)

2. b/k (also has dimension T!)

3. Both of the above

4. None of the above

The speed v of a wave on a tight string depends on the tension in the string T and the mass per unit length . Use a dimensional argument to find v proportional to:

1. /T

2. T/

3. Sqrt(T/)

4. Sqrt(/T)

The function y(x,t) = 1/[(x-5t)2 +0.1] represents:

1. A wave traveling to the right at speed 5

2. Same but speed sqrt(0.1)

3. A standing wave centered at 5

An oscillator consists of a mass hanging from a spring, the mass constrained to move vertically. The oscillator is taken to the moon and set up there (gmoon = 0.2gearth).

1. The period increases by a factor 5.

2. The period stays the same.

3. The period decreases by a factor 5 .

When I jiggle the end of a string to send a wave down, the energy of the wave moving along is

1. Pure kinetic energy, like a moving ball

2. No – there is also potential energy

The speed of sound v in air depends on the air density and the bulk modulus B = (1/V)dP/dV. Use dimensions to establish that v is proportional to:

1. B/2. /B

3. (B/)

4. (/B)

A 3dB increase in sound intensity means a power increase of approximately:

1. 30%

2. a factor of 2

3. A factor of 3

Could someone with excellent hearing hear a sound level of 0 dB?

1. Yes – just possible

2. No – that isn’t any sound at all

A single pulse of sound (pressure) is sent down a tube. The far end is open. Is the pulse reflected at the open end?

1. No

2. Yes

3. Yes, but as negative (below atmospheric) pressure

In the interference pattern from two synchronized point sources, what happens to the number of node lines if the sources are brought closer together?

1. The number increases

2. It decreases

In the interference pattern from two synchronized point sources, what happens to the number of node lines if the oscillation frequency is increased?

1. The number of node lines increases

2. The number decreases

Blue light has shorter wavelength than red light. Is the distance between bright spots in the two slit diffraction pattern smaller or greater?

1. Smaller

2. Greater

For light passing through a single very narrow slit, how does the spread of the bright central spot change if the slit gets even narrower?

1. It gets narrower

2. It gets wider

You are jogging towards a wall at 3.4 m per sec, you whistle at 2000 Hz. The echo you hear from the wall has frequency:

1. 1980 Hz

2. 2000 Hz

3. 2020 Hz

4. 2040 Hz

You are driving at 34 m per sec. Some distance behind you a police car also driving at 34 m per sec is sounding a siren at 1000 Hz. You hear it at frequency:

1. 900 Hz

2. 1000 Hz

3. 1100 Hz

4. 1200 Hz