Physics

Front 1

A heat engine that is 40% efficient and has a heat input of 200 J per cycle at the hot reservoir will waste 80 J of heat each cycle.

Back 1

False

Hint 1

Qh = 200, Qc = 80, W = Qh - Qc = 200 - 180 = 120.

e = W / Qh = 120 / 200 = 0.6

Front 2

A refrigerator increases the entropy of its hot reservoir at the same time as it decreases the entropy of its cold reservoir, but a heat engine does just the opposite.

Back 2

True

Front 3

As you increase the difference between the temperatures of the hot and cold reservoirs, a Carnot engine converts a larger and larger percent of the heat put into work.

Back 3

True

Hint 3

True if 1 - Tc / Th is larger, not just the difference.

Front 4

Heat can be transformed into work with 100% efficiency, but work cannot be transformed into heat with 100% efficiency.

Back 4

False

Hint 4

Reversed.

Front 5

A Carnot engine operating between heat reservoirs at 10 C and 40 C has an efficiency of 75%.

Back 5

False

Hint 5

Tc = 10 C = 283 K, Th = 40 C = 313 K.

emax = 1 - Tc / Th = 1 - 283 / 313 = 9.6 %.

Front 6

If two different gases are at the same temperature, the average translational kinetic energy per molecule must be the same for both of them.

Back 6

False

Hint 6

Only if ideal gases.

Front 7

All real heat engines are less efficient than the Carnot engine.

Back 7

True

Front 8

A 20% efficient heat engine that must do 50 J of work each cycle requires a heat input of 250 J per cycle.

Back 8

True

Hint 8

True

Front 9

Just as a heat engine is more efficient and more effective as its efficiency approaches 1, a refrigerator is more and more effective as its coefficient of performance approaches 1.

Back 9

False

Hint 9

Should be much larger than 1.

Front 10

Water turns to ice when it is placed in a freezer. During this process, the entropy of this water has decreased.

Back 10

True

Front 11

Is temperature a macroscopic or a microscopic concept.

Back 11

Microscopic

Hint 11

Microscopic up to a point; macroscopic where it gets too microscopic.

Front 12

Is liberating heat through combustion a reversible or an irreversible process?

Back 12

Irreversible

Front 13

If the hydostatic pressure at a certain depth in the ocean is 2 atm, the hydrostatic pressure will be 4 atm if you go twice as deep.

Back 13

False

Hint 13

Gauge pressure

Front 14

A long vertical metal cylinder is filled with oil. If a piston pushes on the top of this cylinder and increases the pressure there by 6,000 Pa, the pressure at the bottom will increase considerably more due to the weight of the oil.

Back 14

False

Front 15

According to Pascal's principle, if you increase the pressure enough so that the force at one end of an oil-filled tube increases by 10 N, the force will increase at all points in the tube by 10 N.

Back 15

True

Front 16

When an object is floating, the buoyant force on it is just equal to its weight.

Back 16

True

Front 17

If you increase the pressure on the surface of a can of water, you will increase the buoyant force on objects placed in that water.

Back 17

False

Hint 17

Fb = Density of fluid x Volume of fluid x Gravity = Weight of fluid

Front 18

If the gauge pressure at a certain depth in Lake Michigan is 3.5 atm, the absolute pressure at that depth is 4.5 atm.

Back 18

True

Hint 18

Absolute pressure = Atmospheric pressure + Gauge pressure

4.5 = 1 + 3.5

Front 19

If a uniform sphere is compressed to half of its original diameter, its mass remains the same but its density becomes 8 times as great.

Back 19

True

Hint 19

Vsphere = (4/3) x pi x r^3

Di = 2, Ri = 1.

Df = 1, Rf = 0.5.

0.5^3 = 0.125

Density = mass / Volume

Density = 1 / 0.125 = 8

Front 20

An air bubble underwater has the same pressure as that of the water. As the air bubble rises toward the surface (and its temperature remains constant), the volume of the air bubble:

Back 20

Increases

Front 21

The tires of a car support the weight of a stationary car. If one tire has a slow leak, the air pressure within the tire will _a_ with time, the surface area will _b_ with time, and the net force the tire exerts on the road will _c_ with time.

Back 21

A. Decrease

B. Increase

C. Remain constant

Front 22

A tire of an automobile has a gauge pressure of 30 psi at the top of a mountain, and the air temperature inside the tire is 300 K. The atmospheric pressure at the top of the mountain is 0.7 atm. The car is driven down to sea level, where the atmospheric pressure is 1 atm, and the air inside the tire is heated to 350 K. At sea level, assuming no leaks, the gauge pressure of the tire will be:

Back 22

Higher

Front 23

In England in the Middle Ages an extensive system of canals was used for transportation. Some of these canals crossed over canyons flowing over bridges (viaducts). Suppose that a heavily loaded barge crosses over such a waterway bridge.

Back 23

The force on the barge would not change when the barge passed over.

Front 24

A barge loaded with lumber and iron ore floats in a lock by a dam a closed pool of water like a big swimming pool). If some of the cargo is thrown overboard, the level of water in the lock will:

Back 24

Drop

Front 25

A waitress fills your glass with ice water (containing many ice cubes) such that the liquid water is perfectly level with the rim of the glass. As the ice melts,

Back 25

The liquid-water level remains flush with the rim of the glass.

Front 26

A spherical ball of lead (density 11.3 g/cm^3) is placed in a tub of mercury (density 13.6 g/cm^3). Which answer best describes the result.

Back 26

The lead ball will float with about 17% of its volume above the surface of the mercury.

Front 27

If two different solid metals are at the same temperature, the average translational kinetic energy per molecule must be the same for both of them.

Back 27

False

Hint 27

Only true for ideal gases.

Front 28

Liberating heat through combustion can be an irreversible process if it is done slowly.

Back 28

True

Front 29

Work can be transformed into heat with 100% efficiency, and heat can be transformed into work with 100% efficiency, but only at very elevated temperatures.

Back 29

False

Front 30

If both the length and the diameter of a tube are doubled, the flow rate for a given pressure will remain the same.

Back 30

False

Hint 30

Q = pi x R^4 x P / 8 x viscosity x L = R^4 / L = (1 / 0.5^4) / 1 = 0.0625

Front 31

If the depth of a liquid is doubled, the gauge pressure at the bottom of the fluid will also double.

Back 31

True

Hint 31

Pg = Density x Gravity x Depth

Pg = Depth

Front 32

If the change in pressure through a tube is doubled, the flow rate through that tube will double.

Back 32

True

Hint 32

Q = pi x R^4 x P / 8 x viscosity x L

Q = P

Front 33

If the specific heat of a solid metal is 129 J/(kg * K) and it is melted in a furnace that adds 129 kJ of heat to 1 kg of the metal, its temperature will be increased to 1000K.

Back 33

False