ENERGY

WORK

100

What is work equal to? And what is the equation to work it out.

Work is equal to the change in energy of an object. WORK=ENERGY W=Fd

200

Using the reference table, answer this question. How much work is done if you push with a force of 200N against a wall for 10 seconds?

W=Fd=(200N)(0m)=0J NO WORK IS DONE

300

A delivery clerk carries a 34N package from the ground to 5th floor of an office building (a total of 15m) how much work did he do?

W=Fd=(34N)(15m)=510J

400

A force of 825N is needed to push a car across a lot and two students push the car 35m. 1)How much work is done? 2) After a rainstorm the force needed doubles so by what amount does the work change?

1)W=Fd=(825N)(35m)=28875J 2) W=Fd=(825Nx2)(35m)=57750J difference=57750J-28875J=28875

POWER

100

Define power and state the equation

Power is the rate at which work is done. P=W/T=Fd/t=Fv

200

A man pushes a box with force of 400N and moves it 35m in a time of 20sec, what power does he exert on the box?

P=Fd/t=(400N)(35m)/20s=700Watts

300

A person walks 40m and carries a 25kg backpack up a 15m high hill. 1) What is the work done? 2) if the trip took 35 sec what was the power?

1)W=fd=(250N)(15m)=3750J 2)p=w/t=3750J/35s=107W

400

A 70kg jogger runs up a long flight of stairs in 4sec. The vertical height is 4.5m. 1) Estimate the joggers power output 2) How much energy did this require?

1) P=Fd/t=(700N)(4.5m)/4sec=787.5W 2) W=(700N)(4.5m)=3150J=ENERGY REMEMBER: WORK=ENERGY!!!

KINETIC ENERGY

100

What is the equation to work out KE?

KE=(.5)(m)(v^2)

200

Write out an equation relating work and KE

DeltaKE=W=(.5m)(vf^2-vi^2)=(KEf-KEi)

300

How much work is required to accelerate a 1000kg car from 20m/s to 30m/s?

W=(.5)(1000Kg)((30m/s^2)-(20m/s^2))=250000J

400

A softball, with a mass m = 0.5 kg, is thrown by the pitcher at a speed of 30 m/s. i. What is the kinetic energy of the softball? ii. How much work did the pitcher do on the softball? iii. If her arm acted on the softball over a distance of 1.5 meters, what force did she exert on the softball?

i. KE=(.5)(.5kg)(30m/s)^2=225J ii. W=KE=225J iii. w=fd f=w/d=(225J)/1.5m=150N

POTENTIAL ENERGY

100

Define potential energy

the stored energy of an object resisting its natural state

200

What formula is used to solve for gravitational PE?

APE=mgAh note: A= delta. PEg is always +

300

A 60kg skier starts from rest at the top of a 10m high hill, how much PEg does the skier have at the top?

PE=mgh=(60kg)(10m)(10m/s^2)=6000J

400

A 1000kg train starts from rest at the top of a 200m high bridge, what is the PE?

PE=mgh=(1000kg)(10m/s^2)(200m)=2000000J

CONSERVATION OF ENERGY

100

How do we manipulate the Law of the conservation of energy for a pendulum? hint: what is equal to what

PEtop=Etotal=KEbottom

200

http://library.thinkquest.org/2745/data/pend.gif type in this link andon this diagram where is the KE highest and where is the PE highest?

At the blue and pink balls PE is highest and KE is lowest At the purple ball KE is highest but PE is lowest.

300

What is the formula for solved for the force of a spring? answer this question: what is the spring constant of a spring stretched 5.4cm with a mass of 400g.

Fs=kx k=Fs/x= 4N/.05m=74N/m

400

http://library.thinkquest.org/2745/data/pend.gif on the diagram,the mass of the ball is 10kg, the height is .2m at h and the acceleration due to gravity is 10m/s^2. work out the PE and KE at the blue and pink balls.

blue ball: PE=(10kg)(10m/s^2)(.2m)=20J KE= 0J pink ball: PE=0J KE= (10kg)(10m/s^2)(.2m)=20J BLUE= MAX PE PINK= MAX KE