PE, KE & Mechanical Energy
A skateboarder is standing still at the top of a ramp. Which type of mechanical energy is greatest?
Potential energy
What energy transformation occurs when a lamp is turned on?
Electrical → light
According to the Law of Conservation of Energy, energy cannot be created or ______.
Destroyed
Which type of heat transfer requires direct contact?
Conduction
Which has particles with greater average kinetic energy: a substance at 20°C or one at 70°C?
The substance at 70°C
A ball rolls down a hill and speeds up. What happens to its potential and kinetic energy?
Potential energy decreases and kinetic energy increases.
What energy transformation occurs as a ball falls toward the ground?
Potential → kinetic
In a closed system, what happens to the total amount of energy?
It remains constant.
You feel heat from a campfire without touching it. Which type of heat transfer is occurring?
Radiation
As the temperature of a substance increases, what happens to the average kinetic energy of its particles?
It increases.
A pendulum swings from its highest point to its lowest point. At which location will its kinetic energy be greatest?
At the lowest point.
A battery-powered flashlight is switched on. Name the energy transformation from the battery to the light produced.
Chemical → electrical → light
A falling object begins with 100 J of potential energy and almost no kinetic energy. Just before reaching the ground, approximately how much kinetic energy will it have if no energy leaves the system?
100 J
Water at the bottom of a pot becomes warmer, becomes less dense, and rises. What type of heat transfer does this movement produce?
Convection
Two objects are touching. Object A is 35°C and Object B is 60°C. In which direction will thermal energy transfer?
From Object B to Object A / from warmer to cooler.
A roller coaster has 800 J of total mechanical energy. At one point it has 250 J of kinetic energy.
How much potential energy does it have?
550 J
A student pulls back a toy car and releases it. The stored energy causes the car to move.
What major energy transformation occurred?
Potential → kinetic
A ball moves down a frictionless track in a closed system. Its potential energy decreases as its kinetic energy increases. What happens to the total energy?
It remains constant.
A metal spoon is placed in hot soup. After several minutes, the handle becomes warm. Identify the type of heat transfer AND the direction thermal energy traveled.
Conduction; from the hotter soup toward the cooler spoon.
Material A has a specific heat of 0.80 J/g°C, while Material B has a specific heat of 2.00 J/g°C. Which material requires MORE energy to produce the same temperature change?
Material B
A roller coaster has 1,200 J of total mechanical energy. At Point A, it has 1,000 J of potential energy. At Point B, its potential energy decreases to 300 J.
Assuming mechanical energy is conserved, how much kinetic energy does the coaster have at Point B?
900 J
A roller coaster starts at the top of a hill and moves toward the bottom.
Explain the relationship between its potential and kinetic energy during the trip.
Potential energy is transformed into kinetic energy. As PE decreases, KE increases.
A student says, “When a roller coaster slows down, some of its energy disappears.” Explain why this statement violates the Law of Conservation of Energy.
Energy cannot disappear. It must be transferred or transformed into another form, such as thermal energy.
An ice pack is placed on top of a room-temperature can of soda. Explain how both conduction and convection help cool the soda.
Conduction transfers thermal energy from the warmer soda to the colder ice pack. The cooled soda near the top becomes denser and sinks while warmer soda rises, creating convection currents.
A company needs a material for a container that should heat up quickly.
Which would be the better choice: a material with a specific heat of 0.75 J/g°C or 2.10 J/g°C? Explain.
0.75 J/g°C, because a material with a lower specific heat requires less thermal energy to change temperature.