work power-work energy

Kinetic energy

the energy of an object due to its motion. depend on mass and velocity.

Potential energy

stored energy describes an object that has the potential to move because of its position.

Gravitational potential energy

potential energy associated with an object due to its position relative to the surface of the earth.

depends on

mass and height above the zero level

elastic potential energy

the potential energy in a stretched or compressed elastic object spring, rubber band etc. depends on the distance you stretch or compress it

spring constant

a # that tells how easily a spring will stretch.

states

the total work done on an object is equal to the change in energy for that object

mechanical energy

the sum of kinetic energy and potential energy

conserved quanties

quantity stays remains constant quantity can change from over. a period of time but the amount will always be the same

mechnical energy is not conserved in the presence of

friction.

what is the quanity force x distance and what quanity can this change

work=force x distance - work equals a change in energy

in the vertical direction how can you have postive work

picking an object up.

in the vertical direction how can you have negative work

lowering an object down

in the vertical direction how can you have no work

holding an object at the same height.

which direction are your force and displacement if your work is postive? are you gaining or losing energy.

force and displacement are in the same direction. gaining energy.

which direction are you force and displacement if your work is negative ? are you gaining or losing energy?

force and displacement are in the opposite direction. losing energy.

work is required to lift a barbell. how many times more work is required to lift the barball three times as high?

3 times that amount of work

brandon carries a football for a 30 yard TD. how muhc work did brandon do on the football?

0 J of work. force and displacment were perperndicular to each other. the height of the football did not change.

Two people with the same mass climb the same flight of stairs. The first person climbs the stairs in 25 seconds, and the second person does so in 35 seconds. Which person does more work?

which person produces more power also?

same work b/c they both have the same mass(Fw) and traveled the same distance.

person 1- when you do the same work in less time you have greater power.

what are the two main forms of mechanical energy?

kinetic and potential energy

if you do 100j of work to elevate a bucket of water, what is its gravatational potential energy relative to its starting position.

100j- the work you do is the PE you gained.

a car is speeding up is the kinetic energy increasing or decreasing?

increasing- velocity and Ke are directly proportional

what will be the kinetic energy of an arrow having a potential energy of 50j after it is shot from a bow?

50j- the PE gets converted into KE.

state 1 reason why a rock projected with slingshot will go faster if the rubber is stretched a extra distance.

more distance pulled= more work=more KE=faster leaving the sling shot and will cover more distance when its let go.

does an object with momentum always have energy?

Yes, KE because if it has momentum it must be moving and KE. ,

does an object with energy always have momentum?

no because if it has Pe it doesn’t not have to be moving, and therefore does not have momentum.

if a mouse and a elephant both run with the same kinetic energy, can you say which is running faster.

Yes, the mouse. If they have the same KE but the mouse is smaller in mass, it must be running faster to have the same Ke as the elephant, which is larger in mass and must be running slower.

an astronaut in full space gear climbs a vertical ladder on earth. Later the same astronaut makes the same climb on the moon. in which location does the gravitational potential energy of the astronaut change more?

earth, because there is more gravuity on earth there is more PE on earth then the moon.

what type of energy exists in a rubber band when you stretch it back?

elastic potential energy- exists in any object that can bend, stretch, twist, snap, etc.

true or false: the ice cubes that you put in a glass to cool your soda transfers cold to the soda.

false: heat always gets transfered from hot to cold(not cold to hot)

what is thermal equilibrium?

when two or more objects are mixed. heat will always transfer from hot to cold until both objects reach the same final temperature.

do substances that heat up quickly normally have high or low specific heat capacities.

low specific heat(metals)- takes a short time to gain/lose hear energy

conductor?

Conductors: transfers heat efficiently through a material (low specific heat items like metals)

insulator?

do NOT transfer heat efficiently through a material(high specific heat items like water wood, plastic.

what are the three means of transferring heat energy?

conduction: touching, transfer heat through material (solids)

convection: transfer of heat through liquids or gases (warm rising through the cold)

radiation: no touching, transfer of heat through electromagnetic radiation like sunlight.

which will rewuire more heat? heating a cup of water(small mass) or a pot of water(large mass) by 50 degrees celsius?

pot of water(large mass)- more mass, more heat is required-direct

if an object starts with 200j of Pe on the top of a hill and slides down to the bottom and ends with 120j of Ke how much mechanical energy was lost? what form of energy did this get converted to?

80j of mechanical energy was lost. the loss in mechanical energy was converted into heat energy, also called internal energy, withtin the ground and the object.