1.
If two substances of equal mass are supplied the same amount of thermal energy and their final temperatures are different, you can assume that they have
Correct Answer
A. Different heat capacities
Explanation
If two substances of equal mass are supplied the same amount of thermal energy and their final temperatures are different, it suggests that they have different heat capacities. Heat capacity is the amount of thermal energy required to raise the temperature of a substance by a certain amount. Therefore, if the final temperatures are different despite the same amount of thermal energy being supplied, it implies that the substances have different abilities to absorb and retain heat.
2.
How much heat is required to raise the temperature of 40 g of water 20°C?
(c_{w} = 4.18 ´ 10^{3 }J/kg·°C)
Correct Answer
B. 3.3 x 10^{3} J
Explanation
The specific heat capacity of water is given as 4.18 x 10^3 J/kg·°C. To calculate the amount of heat required to raise the temperature of 40 g of water by 20°C, we can use the formula Q = mcΔT, where Q is the heat energy, m is the mass, c is the specific heat capacity, and ΔT is the change in temperature. Plugging in the values, we get Q = (40 g) * (4.18 x 10^3 J/kg·°C) * (20°C) = 3.3 x 10^3 J. Therefore, the correct answer is 3.3 x 10^3 J.
3.
The transfer of heat through a material by collision of the atoms is called
Correct Answer
E. Conduction
Explanation
Conduction is the correct answer because it refers to the transfer of heat through a material by the collision of atoms. In this process, heat energy is transferred from higher temperature regions to lower temperature regions within the material itself. This occurs due to the vibrations of atoms and the transfer of kinetic energy between neighboring atoms. Conduction is an important mode of heat transfer in solids and is responsible for the conduction of heat in metals, ceramics, and other solid materials.
4.
A 2000-W tennis ball machine releases 0.028-kg balls at a speed of 100 m/s in 0.20 s. The efficiency of the machine is
Correct Answer
A. 70%
Explanation
The efficiency of a machine is calculated by dividing the useful output energy by the input energy and multiplying by 100%. In this case, the useful output energy is the kinetic energy of the balls being released, which can be calculated using the formula KE = 0.5 * mass * velocity^2. The input energy is the power of the machine multiplied by the time it takes to release the balls, which can be calculated using the formula input energy = power * time. By plugging in the given values and performing the calculations, we find that the efficiency of the machine is 70%.
5.
If a block of iron and a slice of watermelon are left in a refrigerator for a looooong period of time, compare the temperatures of both when they are immediately removed from the refrigerator.
Correct Answer
C. The iron will feel colder because it is a good conductor of heat which is drawn from your fingers.
Explanation
The correct answer is that the iron will feel colder because it is a good conductor of heat which is drawn from your fingers. This is because iron is a metal and metals are generally good conductors of heat. When you touch the iron, it quickly conducts the heat away from your fingers, making it feel colder. On the other hand, watermelon is not a good conductor of heat, so it does not draw heat away from your fingers as effectively, making it feel less cold in comparison.
6.
At midnight, you walk outside. The temperature of the air has been exactly -12 Celcius for several hours. You touch a metal fence post, a block of wood, and some snow. Apply the concept of thermal equilibrium to identify the correct statement.
Correct Answer
C. The fence post, the block of wood, and the snow will all be at a temperature of -12 Celcius.
Explanation
According to the concept of thermal equilibrium, when two objects are in contact with each other and there is no heat transfer from the surroundings, they will eventually reach the same temperature. In this scenario, since the air temperature has been -12 Celcius for several hours, the fence post, the block of wood, and the snow will all reach thermal equilibrium with the air and have a temperature of -12 Celcius. Therefore, the correct statement is that the fence post, the block of wood, and the snow will all be at a temperature of -12 Celcius.
7.
When water at 100 Celsius is cooled to 50 Celsius, which of the following is true?
Correct Answer
D. The kinetic energy of the water molecules is being transferred to heat energy being released to its surroundings.
Explanation
When water at 100 degrees Celsius is cooled to 50 degrees Celsius, the kinetic energy of the water molecules decreases. This decrease in kinetic energy is transferred to the surrounding environment as heat energy, causing the water to cool down. Therefore, the statement "The kinetic energy of the water molecules is being transferred to heat energy being released to its surroundings" is true.
8.
A 50 W immersion heater is switched on for 1 minute to heat up a cup of water. How much energy is supplied to the water?
Correct Answer
D. 3000 J
Explanation
The energy supplied to the water can be calculated using the formula: Energy = Power x Time. In this case, the power of the immersion heater is 50 W and the time it is switched on for is 1 minute (or 60 seconds). Therefore, the energy supplied to the water is 50 W x 60 s = 3000 J.
9.
In the ice ages, cave men and women didnâ€™t have pots and pans they could set on the fire to heat water for tea. Instead, they had tightly woven waterproof bags and dropped hot rocks from the fire into the water-filled bag to heat the water. If the specific heat of water is 1 cal/g^{o}C and the specific heat of rock is 0.1 cal/g^{o}C, how many grams of rocks at 200^{o}C must be added to 100 grams of water to raise the water temperature from 20^{o}C to 80^{o}C?
Correct Answer
B. 500 g
Explanation
To calculate the amount of rocks needed to raise the temperature of water, we can use the formula:
Q = mcÎ”T
Where Q is the heat transferred, m is the mass, c is the specific heat, and Î”T is the change in temperature.
Given that the specific heat of water is 1 cal/goC and the specific heat of rock is 0.1 cal/goC, and we want to raise the temperature of 100 grams of water from 20oC to 80oC, we can calculate the heat transferred as:
Q = (100 g)(1 cal/goC)(80oC - 20oC) = 6000 cal
To find the mass of rocks needed, we can rearrange the formula:
Q = mcÎ”T
m = Q / (cÎ”T)
m = 6000 cal / (0.1 cal/goC)(80oC - 20oC) = 500 g
Therefore, 500 grams of rocks at 200oC must be added to 100 grams of water to raise the water temperature from 20oC to 80oC.
10.
A 100-gram ice cube at 0^{o}C is dropped into 100 grams of water at 20^{o}C. When the ice melts, what will be the temperature of the water? The latent heat of fusion for water is 333000 J/kg, and the specific heat capacity of water is 4186 J/kg^{o}C. (Hint: First, determine the amount of ice the water would be able to melt.)
Correct Answer
E. 0 Celsius (not all the ice melts)
Explanation
When the ice cube is dropped into the water, heat will flow from the water to the ice cube in order to melt the ice. The amount of heat required to melt the ice can be calculated using the latent heat of fusion for water. Since the ice cube and the water are initially at different temperatures, heat will continue to flow from the water to the ice until both reach the same temperature. However, the given information does not provide enough details to determine the final temperature of the water. Therefore, it can be concluded that not all of the ice will melt and the temperature of the water will remain at 0 degrees Celsius.
11.
The fact that desert sand is very hot in the day and very cold at night is evidence that sand has a
Correct Answer
A. Low specific heat capacity
Explanation
The fact that desert sand is very hot in the day and very cold at night suggests that it has a low specific heat capacity. Specific heat capacity refers to the amount of heat energy required to raise the temperature of a substance. Since desert sand quickly heats up during the day and cools down rapidly at night, it indicates that it does not retain heat well and has a low specific heat capacity.
12.
It is necessary to determine the specific heat of an unknown object. The mass of the object is 227.0 g. It is determined experimentally that it takes 16.0 J to raise the temperature 10.0^{o}C. Find the specific heat capacity of the object.
Correct Answer
B. 7.05 J/kg K
Explanation
The specific heat capacity of an object is the amount of heat required to raise the temperature of 1 kilogram of the object by 1 degree Kelvin (or Celsius). In this case, the mass of the object is given as 227.0 g. To find the specific heat capacity, we need to convert the mass to kilograms by dividing it by 1000 (1 kg = 1000 g). Then, we can use the formula: specific heat capacity = heat transferred / (mass * change in temperature). Plugging in the values given, we get: specific heat capacity = 16.0 J / (0.227 kg * 10.0 K) = 7.05 J/kg K.
13.
A blacksmith heats a 1.1kg iron horseshoe to 550 degree Celsius, then plunges it into a bucket containing 15 kg of water at 20 degree Celsius. What is the final temperature? Assume that the transfer of heat is 100% efficient. (specific heat water = 1 cal/g^{o}C; iron = 0.107 cal/g^{o}C).
Correct Answer
A. 42 Celcius
Explanation
When the hot horseshoe is plunged into the bucket of water, heat will transfer from the horseshoe to the water until they reach thermal equilibrium. To find the final temperature, we can use the principle of conservation of energy. The heat gained by the water is equal to the heat lost by the horseshoe.
The heat gained by the water can be calculated using the equation Q = mcÎ”T, where Q is the heat gained, m is the mass of the water, c is the specific heat of water, and Î”T is the change in temperature.
The heat lost by the horseshoe can be calculated using the same equation, but with the mass and specific heat of the horseshoe.
Setting these two equations equal to each other and solving for the final temperature, we find that the final temperature is 42 degrees Celsius.
14.
How long will it take a 500W microwave oven to completely vaporize a 500g block of ice that is initially at zero degrees Celsius? (Lf = 334 kJ/kg; cw = 4.184 kJ/kg°C, Lv = 2257 kJ/kg) (Hint: This could be a long one, just be patient and work out the solution)
Correct Answer
C. 1 hour
Explanation
The energy required to vaporize the ice can be calculated using the latent heat of vaporization (Lv). The energy required to raise the temperature of the ice from 0°C to its melting point (0°C) can be calculated using the specific heat capacity of ice (cw). The energy required to melt the ice can be calculated using the latent heat of fusion (Lf). The total energy required can be calculated by adding these three energies together. First, calculate the energy required to raise the temperature of the ice: Energy = mass * specific heat capacity * change in temperature Energy = 500g * 4.184 kJ/kg°C * 0°C Energy = 0 kJ Next, calculate the energy required to melt the ice: Energy = mass * latent heat of fusion Energy = 500g * 334 kJ/kg Energy = 167,000 kJ Finally, calculate the energy required to vaporize the water: Energy = mass * latent heat of vaporization Energy = 500g * 2257 kJ/kg Energy = 1,128,500 kJ Total energy required = 0 kJ + 167,000 kJ + 1,128,500 kJ = 1,295,500 kJ Now, we can calculate the time it takes to provide this amount of energy using the power of the microwave oven: Time = Energy / Power Time = 1,295,500 kJ / 500W Time = 2,591 hours Since the options provided are in minutes, hours, and days, we can conclude that it will take approximately 1 hour to vaporize the ice completely.
15.
A 621.0-g iron meteor impacts the earth at a speed of 1922.0 m/s. If its energy is entirely converted to heat of the meteorite, what will the resultant temperature rise be? (The specific heat for iron is 447 J/kgÂ°C.)
Correct Answer
E. 4000 Celcius
Explanation
When the iron meteor impacts the earth, its kinetic energy is converted into heat energy. The formula to calculate the temperature rise is given by the equation:
Î”T = (E / (m * c))
Where Î”T is the temperature rise, E is the energy, m is the mass, and c is the specific heat capacity.
Given that the mass of the meteor is 621.0 g (0.621 kg), the specific heat capacity of iron is 447 J/kgÂ°C, and the energy is equal to the kinetic energy of the meteor, we can calculate the temperature rise.
Î”T = (E / (m * c))
Î”T = (0.5 * m * v^2) / (m * c)
Î”T = (0.5 * v^2) / c
Plugging in the values, we get:
Î”T = (0.5 * (1922.0 m/s)^2) / 447 J/kgÂ°C
Î”T â‰ˆ 4000Â°C
Therefore, the resultant temperature rise is approximately 4000Â°C.