Chapter 11

Question 1

Kinetic Energy

Answer 1

the energy an object has due to its motion

Question 2

What is the amount of kinetic energy an object has depend on?

Answer 2

mass and speed

Question 3

The formula for kinetic energy

Answer 3

Ek = 1/2 mv^2

Question 4

What is the “Work Energy Theorem?”

Answer 4

The work done to the object quals its change in kinetic energy, or in symbols, W = ΔEk

Question 5

Units for kinetic energy:

Answer 5

Joules

Question 6

When is the work done to an object negative?

Answer 6

When force is opposite to motion because energy has decreased and causes a negative change in Ek

Question 7

Potential energy

Answer 7

The energy stored in an object due to its position, shape or form

Question 8

Examples of potential energy:

Answer 8

e.g. - the gravitational potential energy of a rock lifted up - chemical energy in food or fuels - nuclear energy stored in the nucleus of the atom - electrical energy in wires - elastic energy in a kicked ball, pole vaulter’s pole, spring, tennis racket, etc.

Question 9

What is mass according to Einstein

Answer 9

According to Einstein, mass itself is a form of potential energy -

Question 9

How does a pole vaulter illustrate how energy is converted from one form to another?

Answer 9

• chemical energy from food → kinetic energy of person → elastic potential energy of bent pole → some kinetic and then gravitational potential energy of person → kinetic energy as a person falls → sound and heat when a person lands

Question 10

when we talk about potential energy, what are we really talking about?

Answer 10

Gravitational potential energy, since in this chapter, we are only dealing with potential energy due to an object’s position,

Question 11

Forumla for potential energy:

Answer 11

Ep/Eg = mgh
This only applies near the earth’s surface where we can use the value “g”

Question 12

Units for potential energy

Answer 12

joules

Question 13

Why does W = ΔEp

Answer 13

Just like with kinetic energy, an object can have some potential energy to start with, so really the work done to an object is equal to its change in potential energy.

Question 14

At what position does an object have zero potential energy?

Answer 14

eg. a book held one meter above the desk - Should its height be measured from the desktop?, the floor?, or the ground outside the window? or sea level? * It really doesn’t matter.

Question 15

What is all that matters with potential energy?

Answer 15

While we can quite easily say how much kinetic energy an object has, we can only say how much potential energy an object has relative to whatever reference point you choose. All that really matters is the change in potential energy from one point to another.

Question 16

Law of conservation of energy

Answer 16

Within a close, isolated system, the total amount of energy is constant. It cannot be created or destroyed. It can only be transferred from one object to another or changed from one form to another.

Question 17

Since energy is a scalar, how is it conserved in an explosion? (there is no kinetic energy before the explosion and lots of kinetic energy after)

Answer 17

it is converted from chemical potential energy to kinetic energy.

Question 18

What is mechanical energy?

Answer 18

Gravitational potential energy and kinetic energy together.

Question 19

What equation do you use when speeds approaching the speed of light are involved?

Answer 19

Ek = 1/2mv^2 does not hold true. Instead, we must use equations from Einstein’s Theory of Relativity.