Physical Science Ch. 4

3. A bike and rider have a combined mass of 100.0kg. How many calories of heat are generated in the brakes when the bike comes to a stop from a speed of 36.0 km/h?

first, change 36.0km/h to m/s... you get 10m/s to fine energy given the mass and velocity, use the KE formula: KE = 1/2(m)(v^2) KE = 1/2(100kg)(10m/s^2) KE = 5,000J convert 5,000J to calories for heat: 5,000J / 4.184 J = 1,195 cal, or *1.20 kcal of heat generated*

1 cal =

4.184 Joules (so 1 kcal = 4,184 J)

Q = mLf

Q = mLf heat absorbed or released = mass x latent heat of fusion

Q = mLv

Q = mLv heat absorbed or released = mass x latent heat of vaporization

2. an electric current heats a 221g copper wire from 20℃ to 38℃. how much heat was generated by the current? (Ccopper = 0.093 kcal/kg℃)

Q = mc⏃T first, change 0.093 kcal/kg℃ to cal/g℃... (you end up with the same number) Then, plug numbers into equation: Q = (221g)(0.093cal/g℃)(38 - 20℃) *Q = 370 calories of heat generated*

Q = mc⏃T

Q = mc⏃T quantity of heat = mass x specific heat x temp change

26. Suppose ammonia is spilled in the back of a large room. If there were no air currents, how would the room temperature influence how fast you would smell ammonia at the opposite side of the room? a. Warmer is faster. b. Cooler is faster. c. There would be no influence.

a. Warmer is faster.

The specific heat of copper is 0.093 cal/gC°, and the specific heat of aluminum is 0.22 cal/gC°. The same amount of energy applied to equal masses, say, 50.0 g of copper and aluminum, will result in a. a higher temperature for copper. b. a higher temperature for aluminum. c. the same temperature for each metal. d. unknown results.

a. a higher temperature for copper.

10. The transfer of heat that takes place directly from molecule to molecule is a. conduction. b. convection. c. radiation. d. sublimation.

a. conduction.

13. The energy supplied to a system in the form of heat, minus the work done by the system, is equal to the change in internal energy. This statement describes the a. first law of thermodynamics. b. second law of thermodynamics. c. third law of thermodynamics.

a. first law of thermodynamics.

22. Latent heat is "hidden" because it a. goes into or comes out of internal potential energy. b. is a fluid (caloric) that cannot be sensed. c. does not actually exist. d. is a form of internal kinetic energy.

a. goes into or comes out of internal potential energy

32. Conduction best takes place in a a. solid. b. fluid. c. gas. d. vacuum.

a. solid

Heat is the a. total internal energy of an object. b. average kinetic energy of molecules. c. measure of potential energy of molecules. d. same thing as a very high temperature.

a. total internal energy of an object.

25. The work that a heat engine is able to accomplish is ideally equivalent to the a. difference between the heat supplied and the heat rejected. b. heat that was produced in the cycle. c. heat that appears in the exhaust gases. d. sum total of the heat input and the heat output.

a.difference between the heat supplied and the heat rejected.

17. The temperature known as room temperature is nearest to a. 0°C. b. 20°C. c. 60°C. d. 100°C.

b. 20°C.

27. Which of the following contains the most heat? a. A bucket of water at 0°C. b. A barrel of water at 0°C. c. Neither contains any heat since the temperature is zero. d. Both have the same amount of heat.

b. A barrel of water at 0°C

31. Cooking pans made from which of the following metals would need less heat to achieve a certain cooking temperature? a. Aluminum (specific heat 0.22 kcal/kgC°) b. Copper (specific heat 0.093 kcal/kgC°) c. Iron (specific heat 0.11 kcal/kgC°)

b. Copper (specific heat 0.093 kcal/kgC°)

40. Which of the following has the greatest value for liquid water? a. Latent heat of fusion. b. Latent heat of vaporization. c. Both are equivalent. d. None of the above is correct.

b. Latent heat of vaporization.

42. The second law of thermodynamics tells us that the amount of disorder, called entropy, is always increasing. Does the growth of a plant or animal violate the second law? a. Yes, a plant or animal is more highly ordered. b. No, the total entropy of the universe increases. c. The answer is unknown.

b. No, the total entropy of the universe increases

The specific heat of water is 1.00 cal/gC°, and the specific heat of ice is 0.500 cal/gC°. The same amount of energy applied to equal masses, say, 50.0 g of water and ice, will result in (assume the ice does not melt) a. a greater temperature increase for the water. b. a greater temperature increase for the ice. c. the same temperature increase for each. d. unknown results.

b. a greater temperature increase for the ice.

23. As a solid undergoes a phase change to a liquid, it a. releases heat while remaining at a constant temperature. b. absorbs heat while remaining at a constant temperature. c. releases heat as the temperature decreases. d. absorbs heat as the temperature increases.

b. absorbs heat while remaining at a constant temperature

39. The phase change from ice to liquid water takes place at a. constant pressure. b. constant temperature. c. constant volume. d. all of the above.

b. constant temperature

21. The transfer of heat that takes place because of density difference in fluids is a. conduction. b. convection. c. radiation. d. none of the above.

b. convection

The transfer of heat that takes place by the movement of groups of molecules with higher kinetic energy is a. conduction. c. radiation. b. convection. d. sublimation.

b. convection.

33. Convection best takes place in a (an) a. solid. b. fluid. c. alloy. d. vacuum.

b. fluid

28. Anytime a temperature difference occurs, you can expect a. cold to move to where it is warmer, such as cold moving into a warm house during the winter. b. heat movement from any higher-temperature region. c. no energy movement unless it is hot enough, such as the red-hot heating element on a stove.

b. heat movement from any higher-temperature region

20. Styrofoam is a good insulating material because a. it is a plastic material that conducts heat poorly. b. it contains many tiny pockets of air. c. of the structure of the molecules that make it up. d. it is not very dense.

b. it contains many tiny pockets of air.

12. The heat involved in the change of phase from solid ice to liquid water is called a. latent heat of vaporization. b. latent heat of fusion. c. latent heat of condensation. d. none of the above.

b. latent heat of fusion.

If you want to move heat from a region of cooler temperature to a region of warmer temperature, you must supply energy. This is described by the a. first law of thermodynamics. b. second law of thermodynamics. c. third law of thermodynamics.

b. second law of thermodynamics.

19. The specific heat of soil is 0.20 kcal/kgC°, and the specific heat of water is 1.00 kcal/kgC°. This means that if 1 kg of soil and 1 kg of water each receives 1 kcal of energy, ideally, a. the water will be warmer than the soil by 0.8°C. b. the soil will be 4°C warmer than the water. c. the soil will be 5°C warmer than the water. d. the water will warm by 1°C, and the soil will warm by 0.2°C.

b. the soil will be 4°C warmer than the water.

Internal energy refers to the a. translational kinetic energy of gas molecules. b. total potential and kinetic energy of the molecules. c. total vibrational, rotational, and translational kinetic energy of molecules. d. average of all types of kinetic energy of the gas molecules.

b. total potential and kinetic energy of the molecules.

11. The evaporation of water cools the surroundings, and the condensation of this vapor a. does nothing. b. warms the surroundings. c. increases the value of the latent heat of vaporization. d. decreases the value of the latent heat of vaporization.

b. warms the surroundings.

18. Using the Kelvin temperature scale, the freezing point of water is correctly written as a. 0 K. b. 0°K. c. 273 K. d. 273°K.

c. 273 K.

30. The specific heat of copper is roughly three times as great as the specific heat of gold. Which of the following is true for equal masses of copper and gold? a. If the same amount of heat is applied, the copper will become hotter. b. Copper heats up three times as fast as gold. c. A piece of copper stores three times as much heat at the same temperature. d. The melting temperature of copper is roughly three times that of gold.

c. A piece of copper stores three times as much heat at the same temperature.

41. Which of the following supports the second law of thermodynamics? a. Heat naturally flows from a low-temperature region to a higher-temperature region. b. All of a heat source can be converted into mechanical energy. c. Energy tends to degrade, becoming of lower and lower quality. d. A heat pump converts heat into mechanical work.

c. Energy tends to degrade, becoming of lower and lower quality.

35. What form of heat transfer will warm your body without warming the air in a room? a. Conduction. b. Convection. c. Radiation. d. None of the above is correct.

c. Radiation

15. More molecules are returning to the liquid state than are leaving the liquid state. This process is called a. boiling. b. freezing. c. condensation. d. melting.

c. condensation

43. The heat death of the universe in the future is when the universe is supposed to a. have a high temperature that will kill all living things. b. have a high temperature that will vaporize all matter in it. c. freeze at a uniform low temperature. d. use up the universal supply of entropy

c. freeze at a uniform low temperature

29. The cheese on a hot pizza takes a long time to cool because it a. is stretchable and elastic. b. has a low specific heat. c. has a high specific heat. d. has a white color.

c. has a high specific heat.

37. The great cooling effect produced by water evaporating comes from its high a. conductivity. b. specific heat. c. latent heat. d. transparency.

c. latent heat

36. When you add heat to a substance, its temperature a. always increases. b. sometimes decreases. c. might stay the same. d. might go up or down, depending on the temperature.

c. might stay the same.

The transfer of heat that takes place by energy moving through space is a. conduction. b. convection. c. radiation. d. sublimation.

c. radiation.

On the Celsius temperature scale a. zero means there is no temperature. b. 80° is twice as hot as 40°. c. the numbers relate to the boiling and freezing of water. d. there are more degrees than on the Fahrenheit scale.

c. the numbers relate to the boiling and freezing of water.

External energy refers to the a. energy that changed the speed of an object. b. energy of all the molecules making up an object. c. total potential energy and kinetic energy of an object that you can measure directly. d. energy from an extraterrestrial source.

c. total potential energy and kinetic energy of an object that you can measure directly.

38. At temperatures above freezing, the evaporation rate can equal the condensation rate only at a. very high air temperatures. b. mild temperatures. c. low temperatures. d. any temperature.

d. any temperature

16. The temperature of a gas is proportional to the a. average velocity of the gas molecules. b. internal potential energy of the gas. c. number of gas molecules in a sample. d. average kinetic energy of the gas molecules.

d. average kinetic energy of the gas molecules.

24. A heat engine is designed to a. move heat from a cool source to a warmer location. b. move heat from a warm source to a cooler location. c. convert mechanical energy into heat. d. convert heat into mechanical energy.

d. convert heat into mechanical energy.

The Fahrenheit thermometer scale is a. more accurate than the Celsius scale. b. less accurate than the Celsius scale. c. sometimes more or less accurate, depending on the air temperature. d. no more accurate than the Celsius scale.

d. no more accurate than the Celsius scale.

34. Radiation is the only method of heat transfer that can take place in a a. solid. b. liquid. c. gas. d. vacuum.

d. vacuum

5. a 75.0kg person consumes a small order of french fries (250.0calories) and wishes to "work off" the energy by climbing 10.0m stairway. How many vertical climbs are needed to use all the energy?

[when ppl say they ate 250 calories, they actually mean kcals.] convert 250kcal to joules: 250kcal x 4,184 J = 1,046,250 J consumed find out how many joules needed to make one trip: Work = Fd F = weight = mg Work = (75kg x 9.8m/s^2)(10.0m) Work = 7,350J per trip calculate total trips needed to "work off" food: 1,046,250 J / 7,350J = *142 trips*

11. how much heat is needed to change 250.0g of water at 80.0℃ to steam at 100.0℃?

in this situation, water is A: heat to 100.0℃ and B: completes a vaporization change... so you need TWO Q formulas To find the first Q , use the standard formula: Q = mc⏃T ~ the book tells us that the specific heat (c) of water is 1.00cal/g℃ ~ Q = (250g)(1.00cal/g℃)(20℃) Q = 5,000cal, or *5kcal* To find second Q, use vaporization formula: Q = mLv ~ Lv stands for the latent heat of vaporization, and the book tells us that for water, it is 540 cal/g ~ Q = (250g)(540 cal/g) Q = 135,000 cal, or *135.0 kcal* To get the total final answer of heat (Q) needed, add the two Q's we found: 5 kcal + 135.0 kcal = *140.0 kcal needed*

8. A 300.0 Watt immersion heater is used to heat 250.0 g of water from 10.0℃ to to 70.0℃. about how many minutes did this take?

watt = J/s, so if we find J, we can solve for s when given ⏃T and m, use the Q = mc⏃T formula to find calories which we can then convert to J: Q = mc⏃T ~ the book tells us that the specific heat (c) of air is 1.00cal/g℃ ~ Q = (250g)(1.00cal/g℃)(60.0℃) Q = 15,000 cal convert cals to J: 15,000cal x 4.184 J = 62,800J now that you have found J and W was given to you, you can find s: s = 62,800J / 300 J per s s = 209 s the question ask for the time in minutes, so convert s to minutes: 209 s / 60 s = *3.5 minutes*

how to covert ℉ to ℃ when given ℉

℃ = 5/9(℉ - 32)

how to convert ℃ to ℉ when given ℃

℉ = 9/5(℃) + 32