Physics 201, Midterm Exam 3Nov. 30, 1999

1.

What is the largest value of absolute pressure inside your mouth that will allow you to sip a drink (density = 1 g/cm³) through a straw extending vertically 10 cm from the drink surface to your mouth ?

*a) 100300 Pa
b) 1000 Pa
c) -1000 Pa
d) 102300 Pa
*e) 100299 Pa
(note: there was a typo in the test text, answer e was meant to be 102299; because of this, I allowed both a and e as valid solutions)

2.

You replace the spring of a mechanism with a new one having a spring constant half the original one. For the same force applied to the spring

*a) the new spring will stretch twice as much and the work involved will also double
b) the new spring will stretch half as much, and the work will be half
c) the new spring will stretch twice as much and the work involved will be 4 times bigger
d) the new spring will stretch twice as much but the work involved will be the same
e) none of the above

3.

Two steel balls of different mass and at different temperature are brought into contact. When they reach thermal equilibrium, which one has experienced the larger temperature change ?

a) the hotter one
b) the colder one
*c) the lighter one
d) the heavier one
e) not enough information

4.

The average kinetic energy of individual gas molecules depends only on the ....... of the gas

a) mass
b) volume
c) density
*d) temperature
e) pressure

5.

After a diver jumps off the platform and before he hits the water

a) his linear momentum is constant
*b) his angular momentum is constant
c) his angular velocity is constant
d) all of the above
e) none of the above

6.

A car going over a bump starts vibrating at a frequency of 4 oscillations/second. If you put on the car roof an elephant whose weight is equal to that of the car + driver, when going over the same bump the car will vibrate at

a) 2 oscillations/s
*b) 2.8 oscillations/s
c) 4 oscillations/s
d) 5.6 oscillations/s
e) 8 oscillations/s

7.

Water is a good storage for thermal energy since it has

a) low density
*b) high heat capacity
c) 0⁰C freezing point
d) anomalous heat expansion behaviour at 4⁰C
e) none of the above

8.

A mixture of Oxygen-16 and Nitrogen-14 is in thermal equilibrium. If the rms (root mean square) speed of the Oxygen molecules is 200 m/s, what is the Nitrogen molecules rms speed? (both molecules are di-atomic)

a) 228 m/s
b) 175 m/s
c) 187 m/s
*d) 214 m/s
e) 374 m/s

9.

You can't believe your luck when, at an auction, you buy an apparently solid gold 1.5 kg paperweight for a few dollars ! When at home, you lower it into a beaker of water and observe that the increase in water level corresponds to a displaced volume of 100 cm³. Knowing that the density of gold is 1.93 x 10⁴ kg/m³, you conclude that

a) yes, you made a great purchase
*b) well, it cannot be solid gold, but it does look nice anyway
c) the density is larger than gold, something must be wrong
d) the procedure does not provide enough information to reach any conclusion
e) none of the above

10.

A virus is known to require temperatures exceeding 100⁰C in order to be completely destroyed. Which of the following techniques would not work to remove the virus from contaminated material ?

a) boil it in a pressure cooker
b) boil it in heavily salted water
*c) boil it in a regular pot until all the water evaporates
d) drop it in molten lead (melting point 327⁰C)
e) they would all work

11.

An aluminum cube painted white is exposed to sunlight. If its temperature is about 60⁰C

a) it reflects and emits radiation that are both visible
b) emitted radiation is visible, reflected is not
*c) reflected radiation is visible, emitted is not
d) neither reflected nor emitted radiation are visible
e) not enough information

12.

When stars run out of nuclear fuel, eventually they collapse into incredibly dense objects called neutron stars. Suppose that a sun-sized star (radius = 7 x 10⁸ m) collapses into a 7 km radius neutron star. If the star's rotational period before collapse was 10⁷ seconds (about 116 days), what will be the neutron star's rotational period ?

*a) 1 ms
b) 2 $\pi$ ms
c) 10^-7 s
d) 1 s
e) 1/(2$\pi$) ms

13.

What is the density of carbon dioxide (CO₂, molecular mass 44) at Standard Temperature and Pressure (P = 1 atm, T = 0⁰C) ?

*a) 1.96 kg/m³
b) 3.72 kg/m³
c) 5.03 kg/m³
d) 0.22 kg/m³
e) 7.28 kg/m³

14.

A 12 kg mass attached to a spring is moved 0.4 m away from the position of equilibrium and then released. If the spring constant is 18 N/m, what is the mass maximum acceleration ?

a) 2.67 m/s²
b) 1.50 m/s²
c) 0.33 m/s²
d) 0.49 m/s²
*e) 0.60 m/s²

15.

In your car radiator heat transfer occurs primarily via

a) radiation
b) conduction
*c) forced convection
d) unforced convection
e) phase change

16.

You are told that your systolic blood pressure is 120 mm Hg. This means that

a) the weight of your blood is enough to sustain a 120 mm column of mercury
b) your blood has the same average density as a column of 120 mm of mercury
c) the maximum absolute pressure exerted by the heart is equivalent to the pressure exerted by a column of 120 mm of mercury
*d) the maximum pressure exerted by the heart exceeds atmospheric pressure by an amount equivalent to the pressure of a 120 mm column of mercury
e) the velocity at which your blood moves induces a pressure differential of 120 mm of mercury

17.

When the water is turned on, a two-jet rotating water sprinkler reaches an angular velocity of 5 rad/s in one second. If you approximate the sprinkler as a 200 gram thin rod 40 cm long pivoting around its center, what is the torque exerted by each of the two jets ?

*a) 6.7 x 10^-3 N m
b) 13.3 x 10^-3 N m
c) 26.7 x 10^-3 N m
d) 53.3 x 10^-3 N m
e) 106.7 x 10^-3 N m

18.

Your car windshield is covered with a 1 mm thick layer of ice over a 1.5 m² area. If the ice temperature is at -10⁰C, for how long do you need to run a 1500 watt hair-drier in order to melt it completely?

*a) about 5 and a half minutes
b) 90 seconds
c) 42 seconds
*d) about 6 and a half minutes
e) about 1 minute
(note: two solutions are allowed, depending on whether you use the correct value for ice heat capacity, or, as I had originally in mind, whether you just use the water value of 1)

19.

An adult and a child are sitting on adjacent identical swings. Once they get moving the adult will swing with

a) much greater period
b) much greater frequency
c) exactly the same period
*d) the same amplitude
e) none of the above

20.

When you sweat, the process mainly responsible for taking heat away from your body is

a) radiation
b) convection
c) forced convection
d) conduction
*e) phase change

21.

To balance the weight of a 50 kg St. Bernard dog, a girl uses a 12 meter long plank as a lever. If the maximum force she can apply is 100 N, the pivoting point must be

a) 4 meters from the girl
*b) 10 meters from the girl
c) 8 meters from the dog
d) 4 meters from the dog
e) none of these

22.

A sample of Oxygen gas (molecular mass = 32) is kept in a cylinder with a movable piston. If the piston is moved in such a way that the volume is doubled and the pressure is halved, and the sample initial temperature is 10⁰C, what is the final temperature?

a) 5⁰C
b) 20⁰C
c) 566 K
d) 141.5 K
*e) 283 K

23.

When an ideal fluid flowing steadily through a conduit encounters a bottleneck

a) both speed and pressure increase
b) both speed and pressure decrease
*c) speed increases and pressure decreases
d) speed decreases and pressure increases
e) not enough information

24.

In a harmonic motion, position, velocity and acceleration have all the same sign

a) when going from x = x_max to x=0
b) when going from x = 0 to x = -x_max
c) when going from x = -x_max to x=0
d) when going from x = 0 to x = x_max
*e) never

25.

A 2 kg sample of unkown material is heated to 80⁰C and thrown into 1 kg of water at 24⁰C. Equilibrium is reached at a temperature of 30⁰C. What was the material? (Specific heat capacities, in Cal/(kg ⁰C): Al 0.215, Cu 0.09, Fe 0.11, Pb 0.03, Ag 0.06)

a) Aluminum
b) Copper
c) Iron
d) Lead
*e) Silver