ฟิสิกส์ ม.6.

Explanation
When an object is dropped from a height, it gains potential energy due to its position in the gravitational field. The potential energy is given by the equation PE = mgh, where m is the mass of the object (10 kg), g is the acceleration due to gravity (9.8 m/s^2), and h is the height (20 m). Substituting the given values into the equation, we get PE = 10 kg * 9.8 m/s^2 * 20 m = 1960 J. However, not all of this potential energy is converted into heat energy. Some of it is converted into kinetic energy as the object falls. The kinetic energy is given by the equation KE = 1/2 mv^2, where v is the velocity of the object (15 m/s). Substituting the given values into the equation, we get KE = 1/2 * 10 kg * (15 m/s)^2 = 1125 J. The remaining energy is converted into heat energy, which is equal to the difference between the potential energy and kinetic energy: 1960 J - 1125 J = 835 J. Since 1 J = 1 Joul, the heat energy gained by the object is 835 Joul, which is equal to 835 Joul.

Explanation
To convert ice into water and then to vaporize the remaining water, we need to consider the phase changes and the specific heat capacities for each phase. First, we need to calculate the energy required to melt the ice:

Q1 = mass × specific heat capacity × temperature change
= 2 kg × 336 kJ/kg × 0°C
= 672 kJ

Next, we need to calculate the energy required to heat the melted water to its boiling point:

Q2 = mass × specific heat capacity × temperature change
= 0.5 kg × 4.18 kJ/kg°C × 100°C
= 209 kJ

Finally, we need to calculate the energy required to vaporize the water:

Q3 = mass × latent heat of vaporization
= 0.5 kg × 2260 kJ/kg
= 1130 kJ

The total energy required is the sum of Q1, Q2, and Q3:

Total energy = Q1 + Q2 + Q3
= 672 kJ + 209 kJ + 1130 kJ
= 2011 kJ

Therefore, the correct answer is 2011 kJ.

Explanation
The change in temperature of the iron block can be calculated using the equation Q = mcΔT, where Q is the heat transferred, m is the mass of the iron block, c is the specific heat capacity of iron, and ΔT is the change in temperature. In this case, the heat transferred is equal to the work done on the block, which is given by W = Fd, where F is the force applied and d is the distance traveled. Since the work done is equal to the change in thermal energy, we can equate the two equations: mcΔT = Fd. Rearranging the equation, we have ΔT = (Fd)/(mc). Substituting the given values, we get ΔT = (15 kg)(80 m)/(15 kg)(0.5 kJ/kg - K) = 0.15 K. Therefore, the change in temperature of the iron block is 0.15 degrees Celsius.

Explanation
When 1 gram of charcoal is completely burned, it releases 3.34 x 104 joules of heat energy. The machine uses charcoal as fuel and is used to lift objects weighing 50 kilograms or more to a height of 50 meters. To calculate the amount of charcoal needed, we need to find the total energy required to lift the object. The potential energy can be calculated using the formula PE = mgh, where m is the mass, g is the acceleration due to gravity, and h is the height. In this case, the potential energy is 50 kg x 9.8 m/s^2 x 50 m = 24,500 joules. Since the furnace loses 95% of the heat energy, the total energy needed is 24,500 joules / (1 - 0.95) = 490,000 joules. To find the amount of charcoal needed, we divide the total energy by the energy released by 1 gram of charcoal: 490,000 joules / (3.34 x 104 joules/gram) = 14.67 grams. Therefore, the answer is 14.97 grams.

Explanation
The decrease in thermal energy can be calculated using the equation Q = mcΔT, where Q is the thermal energy, m is the mass of the water, c is the specific heat capacity of water, and ΔT is the change in temperature. Given that the volume of the can is 0.004 m3 and the density of water is 1000 kg/m3, we can calculate the mass of the water to be 4 kg. The change in temperature is 80 - 15 = 65 degrees Celsius. The specific heat capacity of water is 4.18 kJ/kg.K. Plugging in these values into the equation, we get Q = 4 kg * 4.18 kJ/kg.K * 65 K = 1086.0 kJ. Therefore, the correct answer is 1086.0.

Explanation
When the ice is added to the calorimeter, it will absorb heat from the water in the calorimeter until it reaches a thermal equilibrium. Since the ice is at 0 degrees Celsius, it will begin to melt and absorb heat from the water, causing the temperature of the water to decrease. As the ice continues to melt, it will absorb more heat until it completely melts. At this point, the temperature of the water will be close to 0 degrees Celsius. However, since the water in the calorimeter was initially at 70 degrees Celsius, the final temperature will be slightly higher than 0 degrees Celsius, but still close to it. Therefore, the final temperature will be close to 50 degrees Celsius.

Explanation
When the hot coffee is poured into the glass containing the ice, heat is transferred from the coffee to the ice, causing the ice to melt and the coffee to cool down. According to the principle of conservation of energy, the heat lost by the coffee is equal to the heat gained by the ice. Since the mass of the ice is half of the mass of the coffee, the temperature change will also be half. Therefore, the final temperature of the coffee will be approximately 33.3 degrees Celsius.

Explanation
To determine the number of moles of gas, one needs to know the pressure, volume, and temperature of the gas. The pressure and volume are directly proportional to the number of moles of gas according to the ideal gas law. Additionally, the temperature of the gas is also a factor in determining the number of moles, as temperature affects the kinetic energy and therefore the movement of gas molecules. Therefore, the correct answer is "ความดัน , ปริมาตร , อุณหภูมิ" (pressure, volume, temperature).

Explanation
When the volume of a gas decreases while the temperature remains constant, according to Boyle's Law, the pressure of the gas will increase. In this case, the volume of the gas in the cylinder is compressed from 10 cc to 5 cc, causing the pressure to double. Therefore, the pressure of the gas in the cylinder after compression is 2.0 atm.

Explanation
When the pressure of a gas is increased to 3 times its initial value, the volume of the gas decreases by half. This relationship is described by Boyle's Law, which states that the pressure and volume of a gas are inversely proportional when temperature is held constant. Since the temperature is not mentioned in the question, we can assume it remains constant. According to Boyle's Law, if the pressure increases by 3 times, the volume should decrease by 1/3. Therefore, the volume decreases by 50%, which means the answer is 50%.

Explanation
When the temperature of a gas decreases from 27 degrees Celsius to 21 degrees Celsius, the average kinetic energy of the gas molecules decreases. The average kinetic energy of gas molecules is directly proportional to the temperature. Therefore, the energy decreases by 2 percent.

Explanation
The question states that the average kinetic energy of gas A is E. Since the molecular mass of gas A is 4 times that of gas B, the average kinetic energy of gas B would be 1/4 of E. Therefore, the correct answer is E.

Explanation
When the temperature is doubled, the volume of a gas at constant pressure also doubles according to Charles's Law. Since the energy of a gas is directly proportional to its volume, doubling the volume will also double the energy. Therefore, when the temperature is doubled, the total energy of the gas will be 2 joules.

Explanation
The question asks which gas has the highest average rate of effusion at a temperature of 300 Kelvin. The rate of effusion for a gas is inversely proportional to the square root of its molar mass. Since the molar mass of neon is the smallest among the given gases, it will have the highest average rate of effusion. Therefore, the correct answer is neon (นีออน).

Explanation
The question asks for the temperature at which the average molecular rate of hydrogen gas is equal to the average molecular rate of nitrogen gas at a temperature of 300 K. Since the molecular weight of nitrogen gas is 7 times greater than that of hydrogen gas, the temperature at which their average molecular rates are equal would be lower than 300 K. Therefore, the correct answer is 43 K.

Explanation
The ratio of the molecular masses of hydrogen and oxygen is 2:16, which simplifies to 1:8. Since the rate of effusion is inversely proportional to the square root of the molecular mass, the ratio of the rates of effusion of hydrogen and oxygen is the square root of the inverse of their molecular masses, which is 8:1.

Explanation
When 1 mole of gas is heated to 69.9 joules, it will perform 20 joules of work on the piston. According to the first law of thermodynamics, the change in internal energy of the gas is equal to the heat added to the gas minus the work done by the gas. Therefore, the change in internal energy is 69.9 joules - 20 joules = 49.9 joules. Since the internal energy of a gas is directly proportional to its temperature, the temperature of the gas will increase by 49.9/12.5 = 3.992 degrees Celsius. Rounded to the nearest tenth, the temperature increase is 4.0 degrees Celsius.

Explanation
เมื่อแก๊สมีการเปลี่ยนแปลงแบบความดันคงตัวแล้ว พลังงานภายในของแก๊สจะเพิ่มขึ้น 3 หน่วย ซึ่งหมายความว่าพลังงานความร้อนถูกส่งเข้าไปในระบบแก๊สเพิ่มขึ้น 3 หน่วย เนื่องจากการเปลี่ยนแปลงแบบความดันคงตัวจะทำให้พลังงานภายในเพิ่มขึ้น ตามกฎของไอรอนเทรอปี ซึ่งกำหนดว่า เมื่อแก๊สทำงานโดยมีการเปลี่ยนแปลงแบบความดันคงตัว พลังงานภายในของแก๊สจะเพิ่มขึ้น

Explanation
When 1 gram of water is converted into steam, its volume increases to 1671 cubic centimeters at a pressure of 1 atmosphere. The energy required to convert 1 gram of water into steam is 2250 kJ/kg. Since the question asks for the change in energy within the system, we need to calculate the energy required to convert the given volume of water into steam.

Given that the volume of the water is 1671 cubic centimeters, we can calculate the mass of the water using its density (1 gram per cubic centimeter). The mass of the water is therefore 1671 grams.

To calculate the change in energy, we multiply the mass of the water by the energy required to convert 1 gram of water into steam (2250 kJ/kg).

Change in energy = mass of water * energy required per gram
Change in energy = 1671 grams * 2250 kJ/kg
Change in energy = 3759750 kJ

Converting kJ to J, we get 3759750 kJ = 3759750000 J.

Therefore, the change in energy within the system is 3759750000 J, which is approximately equal to 2083 J.