Energy Transformations
Teacher Larisch will project an image of a ball on a string swinging. Name the position at which the ball has the greatest potential energy AND state why.
Position C, because that is the greatest height/highest position
The formula to calculate gravitational potential energy
Ep = mgh
A kid can jump upwards at a speed of 0.5 m/s. If he has a mass of 32 kg, how much potential energy will he have at the top of his jump?
4 J
Convection can only occur in these 2 phases of matter
Gases and liquids (both are fluids)
This type of material has a low specific heat and easily allows heat to pass through it
conductors
Hair dryers and electric stoves both are examples of this type of energy transformation (what type energy goes in? what type of energy is released?)
electrical energy (or electricity) to heat energy (or thermal energy)
The formula to calculate kinetic energy
Ek = (1/2)mv2
How many joules of heat energy are needed to raise the temperature of 20.0 g (0.0200 kg) of aluminum from 22 K to 55 K, if the specific heat of aluminum is 897 J/(kg * K).
592.02 J
When a lamp heats an object, it's an example of what type of heat transfer?
radiation
This type of material has a high specific heat and resists heat energy moving through it
insulators
This technology transforms solar (light) energy into electricity.
solar panels
State the Law of Conservation of Energy in words or mathematically (double points for both!)
Energy is not created or destroyed
Ep = Ek
A 850 g cast iron skillet is heated from 25oC to 120oC. If the specific heat of cast iron is 0.45 J/(g oC), how much thermal energy did the skillet absorb?
36,337.5 J
True or False: when you hold an ice cube, coldness moves from the cube to your hand via conduction
False. Coldness is not real, it is just the absence of heat. Heat moves, not cold.
A student puts a bit of wax on the end of different metal poles and times how long it takes the wax to melt when the other end of the pole is heated. Based on the data, which metal has the highest specific heat?
Copper - 23 seconds
Aluminum - 37 seconds
Brass - 32 seconds
Nickel - 65 seconds
Nickel, because it took more time, and therefore more heat energy, for the metal to get hot enough to melt the wax
What type of energy transformation occurs when you listen to music on a stereo system?
Electrical to sound energy
The gravitational potential energy of a 25 kg person standing on a 200 m high cliff (g = 9.8 m/s2)
(25 kg)(9.8 m/s2)(200 m) = 49,000 J
If you drop a 8.6kg ball from a height of 233 m, how much potential energy did the ball have? (g = 9.8 m/s2)
19,637.24 J
On a cold night, would you rather sleep on the top bunk or the bottom bunk, given what you know about convection?
The top bunk, because hot air rises due to convection, so it should be warmer on the top bunk.
Which of the following materials would be the best insulator for a lunch bag? (double points opportunity: also state why)
Material Specific Heat (J/g°C)
artificial wool 1.357
cotton 1.300
cork 2.000
Cork, because it has the highest specific heat, so it is the best insulator
Describe 3 energy transformations that occur in your car
burning gasoline (chemical --> thermal)
stereo (electrical --> sound)
headlights/brake lights (electrical --> light)
brakes (kinetic --> thermal)
engine (thermal --> kinetic)
battery start (chemical --> electrical --> kinetic)
What is the Kinetic Energy of a 300 kg object that is moving with a speed of 15 m/s?
33750 J
If you drop a ball from a height of 233 m, how fast will the ball be going when it hits the ground?
67.58 m/s
Which of the following statements is incorrect:
a. different materials conduct heat at different rates
b. radiation can only travel in a vacuum
c. convection is caused by thermal expansion
b.
radiation can also travel through matter, though it is the only type of heat transfer that can occur in a vacuum
Copper has a specific heat of 385 J/(kg oC) and steel has a specific heat of 466 J/(kg oC). If you added the same amount of heat energy to 1 kg of each metal, which would be hotter?
Copper, because materials with a lower specific heat will have a greater change in temperature for the same amount of thermal energy change