Units
What are the units of energy?
J
A box slides across a flat surface without changing its height. If I want to describe its energy, what must I include in my system? (Do not include anything superfluous.)
just the box
Alice says "friction destroys the kinetic energy that an object has." Why is she not quite right?
The energy leaves the object but is not destroyed (it becomes heat or sound)
Compare the energy gained by the rock climbers:
-Frank, whose mass is 70 kg, scales 10 m in 40 s.
-Gert, whose mass is 70 kg, scales 10 m in 50 s.
they are the same
What are the units of work?
J
A rock is dropped from a cliff. If I want to use energy to calculate its velocity at the ground, what must I include in my system? (Do not include anything superfluous.)
rock and earth
Bob says "work is stupid, it's just another term for energy." Why is he not quite right?
Work describes the FLOW of energy.
Compare the power of the rock climbers:
-Frank, whose mass is 70 kg, scales 10 m in 40 s.
-Gert, whose mass is 70 kg, scales 10 m in 50 s.
Frank has greater power
What are the units of power?
W
A box slides across a flat surface without changing its height. It encounters a spring and stops. If I want to use energy to calculate the spring's compression, what must I include in my system? (Do not include anything superfluous.)
box and spring
Chris says "power is stupid, it's just another term for energy." Why is he not quite right?
Power is the RATE at which energy flows.
Compare the energy gained by the rock climbers:
-Heidi, whose mass is 55 kg, scales 12 m in 30 s.
-Gert, whose mass is 60 kg, scales 12 m in 30 s.
2000 J
A spring-loaded marble launcher shoots a marble straight up. If I want to determine the height it reaches with energy, what must I include in my system? (Do not include anything superfluous.)
spring marble earth
Debbie is doing an experiment says "this spring is storing 50 J to the right." Why is she not quite right?
Energy does not have a direction.
Compare the power of the rock climbers:
-Heidi, whose mass is 55 kg, scales 12 m in 30 s.
-Gert, whose mass is 60 kg, scales 12 m in 30 s.
Gert has greater power
How many Watts is 0.5 kW?
500 W
A box slides down a ramp. If I want to determine its velocity at the bottom, what must I include in my system? (Do not include anything superfluous.)
box and earth
Eugene says "I hate energy! I'll just solve problems using forces." Give an example of a problem in which energy makes your life easier than forces.
basically anything at an angle
basically anything with variable forces
basically anything where only start and finish points matter
Compare the power of the rock climbers:
-Ingrid, whose mass is 48 kg, scales 10 m in 30 s.
-Jane, whose mass is 60 kg, scales 8 m in 30 s.
They are the same