Part I Multiple Choice Conceptual Questions

EXAM 3 IUPUI Physics 100

Dr. Edward Rhoads Spring 2008

NAME______

Part I – Multiple Choice Conceptual Questions

Directions: Circle for the one alternative that best completes the statement or answers the question. Unless otherwise stated, assume ideal conditions (no air resistance, uniform gravity, etc.) 2 points each

1) A river becomes clogged and as a result backs up. That is to say that the velocity in the middle of the river is negative (upstream). The pressure at the surface of the water in the middle of the river compared to the motionless bank is:

(A) the same (B) the middle has higher pressure

(C) the middle has lower pressure (D) is impossible to compare (E) none of the above

2) An ice cube of mass 10 grams is set into a glass of an unknown liquid which is brim full. If the density of the liquid is 1.25 times the density of water then what is the mass of unknown liquid which spills out of the glass?

(A) 8 grams

(B) 10 grams

(D) all of the liquid will spill out

(E) none of the liquid will spill out

3) Which of the following is the same type of wave as a radio wave?

(A) gamma ray

(B) ocean wave

(D) all of these are the same type as a radio wave

(E) none of these are the same type as a radio wave

4) Which of the following devices allows you to collect charges?

(A) conductor (B) insulator

5) Which of the following devices allows you to limit the flow of charges (but does allow them to flow)?

(A) conductor (B) insulator

6) Which of the following devices allows you to move charges easily?

(A) conductor (B) insulator

7) Which of the following devices allows you to prevent the movement of charges?

(A) conductor (B) insulator

8) Which of the following devices allows you to pump charges to a higher potential?

(A) conductor (B) insulator

9) Two charged objects attract each other with an electric force F. Suppose that one charge is halved and the distance between them is doubled. The new electric force equals

(A) 2F (B) ½F (C) 4F

(D) 8F (E) 1/8 F

10) You have two plastic rods. The first has a length of 10 m and a radius of 0.1 m. The second has a length of 2 m and a radius of 0.5 meters. Which has a higher resonance frequency?

(A) the 10m rod

(B) the 2 m rod

(D) since they are made of plastic, neither rod has a resonance frequency

(E) none of the above

Part II – Word Problems – 20 points each

Directions: Solve each problem using the formulas listed on the last page. Show your work to receive full credit. Box your final answer, clearly label which question it goes with, and record its appropriate unit.

1) In the distant future a spaceship travels to a planet which is completely covered by water. The atmosphere is the same thickness as the earth’s atmosphere and the planet has the same gravity as earth. Water has a density of 1000 kg / cubic meter.

(A) The shallowest depth of the ocean is 2300 meters. What is the pressure at that depth?

(B) If your submarine had a surface area of 17 square meters then what would be the inwards force on the submarine at that depth?

(D) Suppose that the integrity limit of the submarine was 2.3 * 109 N. How deep would the submarine be able to dive? Hint: First find the pressure that would create this force.

A) Pressure = 1 * 105 Pascals [1 + (depth / 10 meters)] = 1 * 105 Pascals [1 + (2300 m / 10 meters)]

Pressure = 2.31 * 107 Pascals

B) Force = Pressure * Area = 2.31 * 107 Pascals * 17 m*m = 3.9 * 108 Newtons inward

C) Buoyancy force = weight of liquid displaced.

Weight = mass * gravity and mass = density * Volume

mass = 1000 kg/cubic meter * 11 cubic meters = 11,000 kg

Weight = 11,000 kg * 10 m/s2 = 1.1 * 105 Newtons = Buoyancy force

D) Pressure = Force / Area = 2.3 * 109 N / 17 sqare meters = 1.35 * 108 pascals

Pressure = 1 * 105 Pascals [1 + (depth / 10 meters)] = 1.35 * 108 pascals

so, [1 + (depth / 10 meters)] = 1350 depth / 10 meters = 1349 so depth = 13490 m

2) A lightning strike carries 5 * 108 J of energy. Let us assume the charge of the ground and sky are equal to each other (but opposite signs). The magnitude of each charge is 5 C. You can treat the charges as point charges, that is 1 large charge in the sky and 1 large charge on the ground.

A) What is the distance the lightning bolt travels?

B) Before the lightning bolt is created what is the electric force on the charge in the cloud due to the charge on the ground?

C) What is the electric field for the charge in the sky?

D) What would the force on a single electron in the atmosphere (ignore the charge in the sky) be due to the charge on the ground – be sure to indicate direction?

E) What is the acceleration on the single electron in the atmosphere (ignore the charge in the sky) be due to the charge on the ground – be sure to indicate direction?

A) Energy = k * charge 1 * charge 2 / distance so, distance = k * charge 1 * charge 2 / energy

distance = 9 * 109 N m2 / C2 *5C * (-5C) / (5 * 108 J ) = 450 m

B) Force = - k * charge 1 * charge 2 / (distance squared) towards charge creating force

Force = -9 * 109 N m2 / C2 *5C * (-5C) / (450m * 450 m) (down)

Force = 1.11 * 106 N down

C) E = -k * charge(causing field) / (distance * distance) (towards charge causing field)

or you can use F = q(force on) * E I will do the later here. So, E = F / q(force on)

since the charge in the sky is the – charge E = 1.11 * 106 N down / (-5C) = -2.2 * 105 N down

D) Force = - k * charge 1 * charge 2 / (distance squared) towards charge creating force

Force = -9 * 109 N m2 / C2 *5C * (-1.602 * 10-19 C) / (450m * 450 m) (down)

Force = 3.56 * 10-14 N (down)

E) F = m a so, acceleration = Force / mass = 3.56 * 10-14 N (down) / 9.11 * 10-31 kg

acceleration = 3.92 * 1016 m/s2 down

3) (diagram taken from a website)

The above diagram is a circuit. R1 = 5 Ohms, R2 = 12 Ohms, R3 = 7 Ohms, and R4 = 8 Ohms.

A) What is the effective resistance of the entire circuit?

B) If the current through the battery (V) is 12 Amps then what is the voltage of the battery?

C) What is the current that runs through R3?

D) What is the voltage drop across the R3 resistor?

A) R = R1 + R2 + R3 + R4 = 5 Ohms + 12 Ohms + 7 Ohms + 8 Ohms = 32 Ohms

B) Voltage = Current * Resistance = 12 Amps * 32 Ohms = 384 Volts

C) same as the rest of the circuit which is 12 Amps

D) Voltage component = Current component * Resistance component

Voltage = 12 Amps * 7 Ohms = 84 Volts

4) Earthquake!

An earthquake actually emits two different types of waves. The waves are a transverse wave and compression wave.

A) If the compression wave to an earthquake is felt in Indy 20 seconds after the actual quake then how far from Indy did the earthquake originate (assume the compression waves move 2000 m/s)?

B) For the compression wave and the transverse wave explain if it would travel completely through the earth including the liquid outer core. Be sure to explain why or why not.

C) Which wave would most likely cause the back and forth shaking that earthquakes are famous for?

D) If the frequency of the compression waves is 25 Hz then what is the period of the waves?

A) d = vt = 2000 m/s * 20 s = 40,000 m

B) The transverse earthquake waves die off pretty quickly when they hit the liquid core (hard to do the side to side in a liquid). So transverse does not go all the way through. The compression waves do in fact go all the way through.

C) Transverse

D) Period = 1 / frequency = 1 / 25 Hz = 0.04 seconds

5) CHALLENGE QUESTION: your instructor has gone batty!

A very fast bat tries to catch an insect which is sitting stationary on a leaf on the ground. Bats use sonar pulses to find their prey. On a warm day the speed of sound in air is 342 m/s. The bat is traveling at 50.1 m/s. You will need to use 3 significant digits for this problem.

(A) If the wavelength of the pulse is 0.0183 m then what is the frequency of the pulse?

(B) What is the wavelength that the prey receives?

(C) Your answer to question b is the wavelength of sound that the prey will reflect. In essence the prey will emit this wavelength of sound back towards the bat. What is the wavelength of sound that the bat receives from the prey?

(D) What is the frequency that the bat gets back and how does it compare to the frequency the bat originally emitted?

A) wave speed = frequency * wavelength

so, frequency = wave speed / wavelength = 342 m/s / 0.0183 m = 18700 Hertz

B) Observed wavelength = Emitted wavelength * [1 – (velocity / wave speed)]

= 0.0183 m * (1 – 50.1 m/s / 342 m/s) = 0.0156 m

C) Observed wavelength = Emitted wavelength * [1 – (velocity / wave speed)]

= 0.0156 m * (1 – 50.1 m/s / 342 m/s) = 0.0133 m

D) frequency = wave speed / wavelength = 342 m/s / 0.0133 m = 25700 Hertz

It is significantly higher

EXAM 3 Formulas and Constants

force = mass * acceleration acceleration = force / mass

mass = force / acceleration

weight = mass * gravitational acceleration

distance = average velocity * time time = distance / average velocity

average velocity = change in position / time

acceleration = change in velocity / time

change in velocity = acceleration * time time = change in velocity / acceleration

distance = 1/2 acceleration * time * time

gravitational acceleration on the surface of the earth = 10 m/s2

change = new – old

momentum = mass * velocity

total momentum = mass * velocity for each object added up

total momentum before collision = total momentum after collision

change in momentum = mass * change in velocity

change in momentum = force * time = mass * change in velocity

work = energy transferred = force * distance

kinetic energy = ½ mass * velocity * velocity

gravitational potential energy = mass * gravity * height

power = work done / time

angular distance = angular velocity * time

velocity (linear) = radius * angular velocity (in radians/second)

angular momentum = inertia * angular velocity

change in angular velocity = angular acceleration * time

Torque = force * distance from rotation point = Inertia * angular acceleration

centrifugal force = mass * velocity * velocity / radius

Gravity Force = G * Mass1 * Mass2 / (distance * distance)

Orbital velocity (sun) = (30 km/s) / [distance (in AU)]1/2

Note: the ½ power is a square root

Escape velocity = 1.4 * orbital velocity

Period2 = constant * semi major axis3

Pressure = Force / Area Force = Pressure * Area

Water Pressure = 1 * 105 Pascals [1 + (depth / 10 meters)]

Density = Mass / Volume Mass = Density * Volume Volume = Mass/Density

Pressure = 1 * 105 Pascal - 1/2 * density * fluid velocity * fluid velocity

Period = 1 / Frequency

Wave speed = wavelength * frequency

Observed wavelength = Emitted wavelength * [1 – (velocity / wave speed)]

k is a constant, and is 9 * 109 N m2 / C2

Electric Field = Force / charge

Force = -k charge1 * charge 2 / (distance * distance)

Potential Energy = k * charge1 * charge 2 / distance

Voltage = Current * Resistance

Voltage for a circuit = Current for circuit * Resistance for Circuit

Voltage for a component = Current for component * Resistance of component

Power = current * voltage

Reff = R1 + R2 + R3 + R4 + …

1/Reff = 1/R1 + 1/R2 + 1/R3 + ….

If only 2: Reff = (R1 * R2) / (R1 + R2)

ibranch = V / Rbranch

itotal = V / Rtotal

magnitude of electron and proton charge = 1.602 * 10-19 C

mass of electron = 9.11 * 10-31 kg

mass of proton = 1.67 * 10-27 kg