Work and Energy

Question 1

Kinetic energy

Answer 1

Energy of motion

Question 2

Potential energy

Answer 2

energy associated with a given objects position in space

potential to do work

Question 3

Elastic potential energy

Answer 3

When a spring is stretched or compressed from equilibrium length

k is the spring constant and x is the magnitude of displacement from equilibrium

Question 4

First Law of thermodynamics

Answer 4

Conservation of mechanical energy

E = U + K

Question 5

Conservative forces + two commonly used in MCAT

Answer 5

Those that are path independent and do not dissipate energy

🔺E = 🔺U + 🔺K = 0

gravitational and electrostatic

Question 6

Nonconservative forces

Answer 6

Friction, air resistance, viscous drag

W_{nonconservative} = ∆ E = ∆U + ∆K

work done by nonconservative forces is the energy “lost”from the system

Question 7

Two ways in which energy can be transferred

Answer 7

Work (J) and heat (∆H)

Question 8

Work

Answer 8

Question 9

Relationship between sign of work and what happens to a gas

Answer 9

1. When work is done by a system (the gas expands pushing the piston) then the work is positive
2. When work is done on a system (the gas compresses due to piston being pushed down) the work is said to be negative

Question 10

Isovolumetric or isochoric process

Answer 10

Volume stays constant and pressure changes. No work is done

you will see a change in temperature

Question 11

Isobaric

Answer 11

Question 12

Isothermal

Answer 12

Question 13

Power

Answer 13

Rate at which energy is transferred from one system to another

unit: J/s or W

Question 14

Work-energy theorem

Answer 14

Net work done by forces acting on an object will result in an equal change in the object’s kinetic energy

Question 15

Mechanical advantage

Answer 15

Ratio of magnitudes of the force exerted on an object by a simple machine (F_out) to the force actually applied on the simple machine (F_in)

reducing the force needed to accomplish the same amount of work costs increased distance (include ramp vs lifting)

Question 16

Explain pulley system

Answer 16

The weight (load) is balanced by the total tension in the ropes. Tension on each rope is equal, thus each rope supports half the weight. Only half the effort is required to lift the weight. BUT you need double the load distance as the effort distance

Question 17

Efficiency

Answer 17

Question 18

Difference between mechanical advantage and efficiency

does adding more pulleys increase efficiency?

Answer 18

Mechanical advantage is the ration of forces. How much force you get from the machine from the force you provided. Ex: pushing a block up a hill requires less force

efficiency is the ratio of work you get over the amount of work done by you. Ex: increasing the number of pulleys increases the effort distance, making it less efficient (increasing d means increase in W). On the other hand, it requires less force to lift the object, therefore there is a greater mechanical advantage