Unit 4 - Energy (20-28%)

Question 1

What’s a system?

They should be treated like ___.

Answer 1

An object or collection of objects (your definition of what your forces are respective to)

They have no internal structure (e.g. like it’s solid)

Question 2

The two ways systems can interact:

Answer 2

• A force is exerted by the objects outside the system or between objects within the system
• A transfer/exchange of some quantity with objects outside the system or between objects within the system

Question 3

Work

Answer 3

The transfer of energy to or from a system through the process of a force being applied over a displacement (a force applied that is external to the system)

Question 4

Work is based on ___ and ____

Answer 4

the amount of force applied on the object and the displacement of the object

Note: if f and d are in the same direction, work is equal to fd. If not, break f into components (cos(x))

Question 5

Unit for work:

Answer 5

Joules (J)

Question 6

If the angle > 90, work is ___.
If the angle < 90, work is ___.
If the angle = 90, work is ___.

Answer 6

Negative
Postive
Zero

Question 7

Energy

Answer 7

The ability to do work, or the quantitative property that must be transferred to an object in order to perform work on that object

Question 8

Kinetic Energy is:

Two things that make it larger:

Answer 8

energy to do the motion of an object

greater speed and greater mass

Question 9

Potential Energy

Answer 9

energy an object has stored with the ability to do work due to its position relative to some “zero” position,

Question 10

Gravitational Potential Energy is:

Three things that make it larger:

Answer 10

potential energy an object has due to its position within the gravitational field of a massive object, like a planet

mass, height above ground, and gravitational field strength

Question 11

Elastic Potential Energy is:

Two things that make it larger:

Answer 11

potential energy of an elastic object caused by a force used to deform that object

amount of stretch/compression and the strength of the elastic

Question 12

Mechanical Energy

Answer 12

The energy an object possesses due to its motion and position. The sum of kinetic energy and the potential energy of a body/system

Question 13

There’s a direct relationship between work and ____.

What force changes kinetic energy?

Answer 13

kinetic energy (work is positive, KE is positive, and vice versa)

only the component of a force parallel to displacement changes kinetic energy

Question 14

Equation for work and kinetic energy

Answer 14

work = change in K
(Fdcos(x) = 0.5m(v final)^2 - 0.5m(v initial)^2

Question 15

If positive work occurs, ME ___.
If negative work occurs, ME ___.
If no work occurs, ME ___.

Answer 15

increases
decreases
doesn’t change

Question 16

Law of Conservation of Energy

Answer 16

If no work is done on a system by an outside force, then the total mechanical energy of a system remains constant

Question 17

Overall Takeaways for Physics

Answer 17

• Don’t forget basic math (trig, circle radius, etc.)
• Don’t assume the answer based on logic, must make sense with equation

Question 18

What doesn’t matter when considering free fall of objects?

What stays the same regardless of the mass of free fall objects (if everything else is the same)?

Answer 18

mass

the velocity

Question 19

The angle for cosine in the work equation is between the _____ and ____.

Answer 19

force, displacement of the object

Question 20

An object in a system by itself can only have _____.

Answer 20

kinetic energy

Question 21

Unit for the spring constant (k):

Answer 21

Newton meters (n/m)

Question 22

If all energy (like kinetic or potential) are increasing or decreasing, then ____.

Answer 22

mechanical energy is increasing or decreasing

Question 23

The area of a force vs. displacement graph is the ___.

Answer 23

work