PHYSICS 110 – Exam #3

Name:_______________________________ Total: ______/100

Each multiple choice question is worth 4 points – you must circle the most correct

answer (2 points) and explain your reasoning (2 points).

1. Assuming a constant temperature, if the volume of a gas increases, then

the pressure on the gas

A. increases

B. decreases

C. stays the same

Carefully explain your reasoning and/or the equation you used for your answer.

2. Consider a proton and an electron that are placed near one another with

no other objects close by. They would

A. accelerate away from each other.

B. accelerate toward each other.

C. remain motionless.

Carefully explain your reasoning and/or the equation you used for your answer.

3. If a wave’s frequency increases, then which statement is always true?

A. The speed of the wave decreases.

B. The amplitude of the wave will increase.

C. The wavelength of the wave will increase.

D. The period of the wave will decrease.

Carefully explain your reasoning and/or the equation you used for your answer.

R

1

R

2

V

10V

A

R

3

For the 2 short answer/ranking questions, you will use the information from the

picture and table to answer the questions. You must show your work (2 points),

rank the letters correctly (1 point) and carefully explain your reasoning and/or the

equation you used for your answers (1 point).

1. In the picture below, a 10 Volt battery is connected to 3 resistors R1, R2,

and R3 in a series circuit with various resistances as given in the table

below. Rank the combinations in order from highest current to lowest

current in Amps for each combination.

2. Rank the combinations of resistors on the basis of the reading on the

voltage from the voltmeter for R1 only from lowest voltage to highest voltage.

Combination A B C D E F

R1 value 3 4 2 4 5 1

R2 value 1 5 3 2 1 3

R3 value 2 6 4 1 3 2

For the problems, you must start with a standard physics formula from the

equation sheet provided. All work must be shown for partial credit.

1. (8 points) Three resistors have values of *R*1=6.0 Ohms, *R*2=5.0 Ohms, and

*R*3=3.0 Ohms.

a. What is their total resistance when connected in parallel?

b. How much current will be drawn from a 12 V battery if it is

connected to the circuit?

2. (8 points) In a dangerous chemistry experiment, you are melting a 4.00 kg

piece of gold with a specific heat of 129.1 J/kg K. If the temperature is

raised from 336 K to 1336 K (the melting point of gold) what is the total

heat in Joules needed to melt the gold if the latent heat of fusion is 1.578 x

106 J/kg?

3. (8 points) If an LED bulb has a voltage of 12 V and a power of 4.2 W, find

the current and resistance of the bulb.

4. (8 points) Suppose you are at Mission Beach and you find a message in a

bottle. The air in the bottle is initially at a pressure of 1 x 105 Pascals and

has a temperature of 303 K. You decide to place the bottle over the fire in

the fire pit to push the cork out. If the temperature in order to eject the cork

is 372 K, what is the final pressure in Pascals of the bottle?

5. (8 points) The density of a 6.8 kg mass iron block is 7870 kg/m3. What is

the buoyant force exerted on this block when it is completely submerged

in water of density 1000 kg/m3?

6. (8 points) Three individuals stand with all of their weight on the heel of one

foot: a man of weight 600 N and a heel area of 0.1 m2, a child of weight

200 N and a heel area of 0.0025 m2, and woman of weight 450 N and a

heel area of 2 x 10-4 m2

a. What pressure does each person exert in Pascals (or N/m2)?

b. Rank the people in order from greatest pressure to least pressure.

7. (10 points) Suppose we have three charges (one negative charge

surrounded by two positive charges as seen below). Charge A is 0.18

Coulombs, Charge B is 0.43 Coulombs, and Charge C is 0.25 Coulombs.

Given the picture below,

a. find the electrostatic force between charges A and B

b. find the electrostatic force between charges B and C

c. What is the net force among the charges and which charge is

the electron more attracted to (A or C)?

3 m 7 m

A B C

8. (10 points) The Brad Pitt star has a temperature of 6000 °F.

a. How many degrees Celsius is it?

b. How many degrees Kelvin is it?

c. The Sun’s temperature is 5800 K…how much hotter or cooler in

Kelvin is this star than the Sun?

9. (8 points) Suppose I want to jump rope for fun and I find a 488 cm jump

rope. Since I am by myself I decide to tie one end of the 5.00 kg rope to a

heavy object so it is fixed. If I apply 65.0 N worth of tension in the rope

along with generating a wavelength of 0.57 m for the waves, what is the

speed of the waves on this rope and what is the frequency of the waves?

10.(4 points) If a physics experiment is measuring two electrons (each having

a charge of 1.6 x 10-19 Coulombs) that are separated by 40 cm, what is the

electrostatic force between the electrons?

11.(Extra Credit problem worth 6 points): Using the same two electrons from

question 10 (each having a mass of 9.1 x 10-28 g),

a. find the gravitational force between the two electrons.

b. How many times bigger or smaller is the electrostatic force

compared to the gravitational force?

Formulas and constants needed for Exam 3:

g = 9.8 m/s2 G = 6.67 x 10-11 N m2/kg2

100 cm = 1 m, 1000 g = 1 kg

Coulomb’s constant (k) = 9.0 x 109 N m2/C2

*T*K *= T*C + 273

*T*C *= T*K – 273

*T*F = 1.8*T*C + 32

*T**C **= *(*T*F – 32) / 1.8

(Tc = Celsius temperature, TF = Fahrenheit temperature, TK = Kelvin

temperature)

Area

Force

Pr essure =

volume

mass

density =ρ 2 21

r

GM M

F =

Q(heat) = mcΔT (m = mass, c = specific heat, ΔT = temperature change)

*Q**melt **= mL*fusion *+ mc*∆*T*

*Q**boil **= mL*vaporization *+ mc*∆*T*

*Q**melt and boil **= mL*fusion *+ mL*vaporization *+ mc*∆*T*

*F**Buoyancy **= ρ**fluid **gV**submerged *(if sinking)

*F**Buoyancy *= mass of object x g [e.g. weight] (if floating)

wave speed = wavelength/period = frequency x wavelength

Ideal Gas Law:

FElectrostatic = (kq1q2) / r2 (q = charge)

Current (I) = charge/time (Coulomb/second or Amps)

Voltage (Volts) = Current (Amps) x Resistance (Ohms)

Power (Watts) = IV = I2R

Rseries = R1+R2+R3+…

1/Rparallel = 1/R1+1/R2+1/R3 + …

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