Warmup:

1
Warm-up

• What is the kinetic energy of a charging rhino
  that has a mass of 1500 kg and a velocity of 5
  m/s?
• What is the potential energy of a 2 kg water
  balloon held off of an 80 m tall building?
• Is it possible for one object to have both KE and
  PE at the same time? If so, give an example.

2
Work, Power, and Energy Continued...
3
A quick recap

• Energy is possessed by an object.
• Work is done when energy is transferred from one
  object to another.
• In other words, work is a measurement of how much
  energy was gained or lost by an object.
• Energy transferred into work
• When would W KE?
• When would W PE?

4
Example 1

• A 1 kg soccer ball reaches a maximum height of 30
  m after a goalies drop kick. How much work
  could the ball do on a midfielders head?
• W PE (the work it can do is equal to its
  energy)
• W mgh
• (1kg)(10m/s2)(30m)
• 300J

5
Example 2

• When a certain car locks up the brakes and
  slides, it has a frictional stopping force of
  2500 N. If the car has a mass of 1000 kg, how
  far will the car slide if it slams on the brakes
  traveling at 10 m/s?
• W KE (the brakes have to do work to stop the
  cars KE)
• F?d ½ mv2
• (2500N) d (1/2)(1000kg)(10m/s)2
• 2500 d 50,000
• d 20m

6
Practice problems

• A car smashes into a stationary cow while
  traveling at 10 m/s and does 62,500 J of work on
  the cow. How much mass does the car have?
• W KE (the work the car can do is
  equal to its KE)
• 62,500J ½mv2
• 62,500J ½ m(10 m/s)2
• m 1250kg
• A baseball catcher applies 640 N of force to stop
  the incoming fastballs thrown by his pitcher.
  When the pitcher throws a fastball, it knocks the
  catchers glove back .25 m before completely
  stopping the ball. If a baseball has a mass of
  .2 kg, how fast is the pitchers fastball?
• W KE (the work required to stop the ball
  is equal to its KE)
• F?d ½mv2
• v 40 m/s

7
Internal Energy

• Definition energy due to the random motion of
  molecules.
• Also called thermal energy, because
• High temperature large internal energy
• Low temperature small internal energy
• Even ice at 0? C has a fairly large amount of
  internal energy.
• Zero internal energy -273? C (this is absolute
  zero - the lowest possible temperature)

8

• Internal energy is a combination of KE and PE on
  a microscopic scale, which makes it impossible
  for us to measure individuallywe need to use
  temperature as an indicator of internal energy.
• Cold is simply the absence of internal energy.
• Cold cannot flow into something, you can only
  remove energy from it to lower its temperature.
• Example A refrigerator doesnt put coldness into
  the food, it removes energy from the food.

9
Heat

• Definition a transfer of energy that results in
  a change in temperature.
• Heat is another measurement of energy, so it has
  units of Joules.
• Just like we said with Work, an object cannot
  contain heat. Instead, we say that heat is
  transferred whenever there is a temperature
  change.
• Heat always flows from an object with higher
  internal energy to something with less internal
  energy.
• An object has energy, an object can do work. An
  object has energy, an object can transfer heat.
• (Biological Energy)

10
Application Problems

• 1) How many times would you have to lift a 10
  pound weight (equivalent to about 50 N of force)
  through a distance of 1 m in order to burn 1
  Calorie?
• (about 83 times)
• 2) How many Calories did you burn in the Harvard
  Step Test?
• (your work/4186)
• 3) How many minutes would you have to keep
  stepping in order to burn off a 280 Calorie
  Snickers bar?
• (280/above answer)
• This would be pretty bad news if we had to burn
  all our Calories by doing mechanical work. What
  are some other ways that our bodies use energy?
• (Think about the fact that our body temperature
  is maintained at 98.6 degrees.)

11
Human Metabolism

• Even when inactive, an average adult male has a
  basal metabolism rate of 90 W!!! That means he
  burns over 1850 Cal per day just by being
  alive!!!
• Calculating Basal Metabolic Rate (BMR)(Enter
  pounds, inches, and years into your equation)
• Males 66 (6.23W) (12.7H) - (6.8A)
  Cal/day
• Females 655 (4.35W) (4.7H) (4.7A)
• Multiplication Factors
• 1.2 little or no exercise
• 1.375 (light exercise, 1-3 days per week)
• 1.55 (moderate exercise, 3-5 days per week)
• 1.725 (heavy exercise, 6-7 days per week)

12
The Biological Process

• Whenever fats, carbs, or proteins enter our body,
  they are broken down into the chemical glucose.
  Everything else gets dumped to the large
  intestine for elimination.
• Glucose is the greatest common denominator of
  biological energy.
• Whenever we do not use all of the energy that we
  have consumed, our body builds the extra glucose
  into fat, because fat is the most efficient means
  of storing energy.
• If the bodys extra energy was stored as carbs
  instead of fat, then cellulite would take up 3
  to 4 times as much space as it does now!! (but
  it would also burn off at a faster rate).