Energy Transformations Review

Q.1)  Which of the following is a conversion from chemical energy to thermal energy? A. Coal is burned to boil water. B. Food is digested and used move arms during a workout.   C. Gasoline is burned to drive a car.   D. All of the above.

A

Q.2)  Which of the following is the best example of increasing an object's potential energy? A. rolling a bowling ball   B. turning on a light bulb   C. stretching a rubber band   D. dropping a pencil

C

Q.3) An object that has kinetic energy must be... A. lifted above earth's surface.   B. in motion.   C. at rest.   D. None of the above.

B

Q.4)  An example of electrical energy being transformed to thermal energy is… A. A radio speaker B. A turbine in a hydro electric dam C. A heater in a car D. A radiator in a home

D

Q.5) Sound energy is... A. The energy of an object’s forward motion. B. The energy caused by an object's vibrations. C. The energy of atomic bonds D. The energy of rotation.

B

Q.6) What device converts chemical energy to mechanical energy? A. human   B. car   C. jet ski   D. All of the above.

D

Q.7) As height increases, so does... A. thermal potential energy B. chemical potential energy   C. elastic potential energy D. gravitational potential energy

D

Q.8) Which example obeys the law of conservation of energy? A. A pendulum swings higher than its starting position B. An object slides across sandpaper at a constant speed  C. A running machine with lots of moving parts remains at a constant temperature. D. A rolling ball make it partway up a hill before coming to a stop and rolling back down.

D

Q.9)  According to the law of conservation of energy, in theory, a bouncy ball should never stop bouncing. However, we know that it eventually stops. Where does the energy go?  A. some gets converted into sound energy and escapes into the surroundings.   B. some gets converted into thermal energy and escapes into the surroundings.   C. some is converted to sound and some is converted to heat but the ball absorbs both of these. D. Both A and B

D

Q.10)  Energy is...   A. when the surfaces of two objects rub against each other.   B. the ability to change position or situation. C. the amount of heat and movement of an object. D. How much speed an object has divided by the time.

B

Work or no work? Crazy Larry is HOLDING the dynamite plunger NO WORK! Crazy Larry PUSHES the plunger WORK!

Work or no Work? Fire erupts, but cow doesn’t move… Smelly, but no work…

Work or No Work? Force is UP but motion is FORWARD No WORK!

Work & Energy an alternative way of viewing motion One of the simplest forms of energy is kinetic energy or energy of motion. When an object is moving it is said to posses a certain amount of kinetic energy that depends on how fast it is moving. The faster an object moves the more kinetic energy it has. Kinetic energy = K = ½ ms2 Kinetic Energy is generally measured in Joules.

Work Work is a transfer of energy into or out of an object. Think about when you do work. It causes you to lose energy because the energy you had has gone elsewhere. In order for work to be done, a force has to be applied to an object and the object has to move a distance. W=Fd (work equals force times distance)

Work and Kinetic Energy Work is measured in joules, just like kinetic energy is measured in joules. When work is done to an object it either gains or looses its K. (speeds up or slows down) W=ΔK

Questions If you push on a wall are you doing work? Not unless the wall moves somewhere or changes its kinetic energy (speeds up or slows down). If you put a 40 N force on a cart to push it 3.0 m. How much work did you do? W = Fd = (40 N)(3.0 m) = 120 J How much kinetic energy did you give the cart? 120 J

Power Power is the rate at which work is done. If you do a certain amount of work fast, you have a lot of power. If you do it slow you have little power. P=W/t (power is measured in J/s or Watts)

Gravitational Potential Energy Sometimes an object can have energy in it but it isn’t moving. For example: a book high up on a shelf. If the book falls it gets faster and faster on the way to the ground. It’s kinetic energy increases, but where did that energy come from? Work was done on the book by the force of gravity. Gravity transferred energy from a stored form called gravitational potential energy and turned it into kinetic energy.

Gravitational Potential Energy Gravitational potential energy is written with the variable U. The more height (h) an object has the more U it has. Larger masses can hold more potential energy. U=mgh (g = 9.8m/s2) Potential energy is measured in Joules like any type of energy

Energy is Conserved