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joejo

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**Thermal Energy Look Over!**

bugeye:

Hi I was wondering if someone could just quickly look over my answers, as I taught myself this lesson on thermal energy and want to make sure I have done the work right. Below I have placed the questions with the answers directly below them. Thanks in advance... :!)

1. The transfer of thermal energy is known as: ?

**heat**

2. The measure of the average speed of the molecules in a substance is known as: ?

**Temperature**

3. The lowest temperature possible has a value of: ?

**0 K or 0 °R (−273.15 °C or −459.67 °F)**

4. When 1 kg of water at 1000C is mixed with 10 kg of water at 00C, the equilibrium temperature will be:

**exactly 100°C**

5. Two objects, A and B, have the same mass and the same initial temperature. However, object A has a smaller specific heat capacity than object B. If the same amount of heat of heat is added to each object, then:

**object A will have the higher final temperature**

6. Two people, Tony and Tania, are employed in a store where they lift heavy objects. Tony can do twice as much work as Tania in twice as much as time. How do their power ratings compare?

**they are equal**

7. A metal absorbs 1200 J of heat energy from its surroundings and then does 700 J of work back on its surroundings. Calculate the change of energy for the metal. ?

**Answer:**

Energy absorbed = change of internal energy + work done

Change of energy = Energy absorbed - work done = 1200 – 700 = 500 J

Change of energy = 500 J

Energy absorbed = change of internal energy + work done

Change of energy = Energy absorbed - work done = 1200 – 700 = 500 J

Change of energy = 500 J

8. The temperature of O2 is measured to be 273.15 ° C. What is this temperature measured in Kelvin?

**Answer: 273.15oC = 273.15 + 273.16 = 546.31 K**

273.15oC = 546.3 K

273.15oC = 546.3 K

9. Amy pours 1 kg of water at 7.0 ° C into a bowl. Calculate the amount of heat energy needed to bring this water to a boil. The specific heat for water is 4186 J/kg. ° C.

**Answer: Heat energy = mc(Tf-Ti) = 1*4186*(100-7) = 4186*93 = 389298 J**

Heat energy needed = 389298 J

Heat energy needed = 389298 J

10. A block made of an unknown substance has a mass of 1.5 kg and a temperature of 15.0 ° C. When 2.6 x 104 J of heat is added to the block, its temperature rises to 90 ° C. Calculate the specific heat capacity to the unknown substance.

**Answer: Specific heat capacity, c = Q/[m(Tf - Ti)]**

= (2.6*104)/[1.5*(90 - 15)] = 231.11 J/KgoC

Specific heat capacity of the unknown substance = 231.11 J/KgoC

= (2.6*104)/[1.5*(90 - 15)] = 231.11 J/KgoC

Specific heat capacity of the unknown substance = 231.11 J/KgoC

11. Calculate the amount of heat energy required to melt a 10 kg block of ice at 0° C into liquid water at 0 ° C. The latent heat of fusion for water is 3.34 x 105 J/kg.

**Answer: Heat energy = mLf = 10*(3.34*105) = 3.34*106 J**

Heat energy required = 3.34*106 J

Heat energy required = 3.34*106 J

12. Calculate the amount of heat energy required to boil 1.0 kg of water at 100 ° C into steam at 100 ° C. The latent heat of vaporization for water is 2.26 x 106 J/kg.

**Answer: Heat energy = mLv = 1*(2.26*106) = 2.26*106 J**

Heat energy required = 2.26*106 J

Heat energy required = 2.26*106 J

13. An elevator motor lifts the elevator full of passengers to a height of 12 m in 30 s. If the mass of the elevator and passengers is 1000 kg, what is the power developed by the motor?

**Answer: Force = mg = 1000*9.8 = 9800 N**

Work done = Force*distance = 9800*12 = 117600 J

Power = Work done / time = 117600/30 = 3920 W

Power developed by the motor = 3920 W = 3920 J/s

Work done = Force*distance = 9800*12 = 117600 J

Power = Work done / time = 117600/30 = 3920 W

Power developed by the motor = 3920 W = 3920 J/s

14. The efficiency of an incandescent light bulb is only 4.0%. Calculate the amount of electric energy that must be input to the bulb in order to get 100 J of light energy from the bulb.

**Answer: input electric energy = output light energy/efficiency = 100/0.04 = 2500 J**

Input electric energy = 2500J

Input electric energy = 2500

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