Good Afternoon!Today we will: review what we learned last week write a short constructed response take notes and solve some energy problemsPlease do before the tardy bell: find a calculator look over your notes from Thursday – pay special attention to the relationship between: work done & kinetic energy stopping distance and force of impact
Warm-UpYou’ve had five minutes to lookover your notes – now it’s time toreviewGet out a single sheet of paper andnumber to five.
Warm-Up Quiz1. If a chair at rest has work doneon it that results in the chair having650 J of kinetic energy, how muchwork was done?
Warm-Up Quiz2. If a bowling ball had 1000 J ofenergy as it entered the balldelivery chute, and 200 J of energyas it leaves the delivery chute, howmuch work was done?
Warm-Up Quiz3. A box is pushed across the floor,giving it a kinetic energy of 800 J. Ifthe force applied was 200 N, howfar did the box travel?
How does cushioning decrease the severity of the damage of a car crash?Proficient answers will include:1. The relationship between kinetic energy and work done2. the relationship between the impact force and the stopping distance3. scientific languageAdvanced answers will include: All of the above PLUS your own math examples
Speed and Kinetic EnergyKE = ½ mv2To safely stop a car traveling 9 m/s(~ 20 mi/h), you will need about 6mof stopping distance.If you triple the speed (27 m/s or60 mi/h), what would yourstopping distance be?
Speed and Kinetic EnergyKE = ½ mv2If you triple your speed, youincrease your KE 9x’s.Why?
Mass and Kinetic EnergyWhich requires more force to stopin 12 m, a 1000 kg passenger carmoving at 8 m/s or a 2000 kg utilityvehicle moving at 6m/s?
Kinetic Energy and DamageRemember: The total amount of kinetic energy is the total amount of work that can be done In terms of a car crash, “work done” is the damage
Kinetic Energy Problem #1a 70.0 kg person is traveling in acar going 13 m/s (~ 29 mi/h).What is the person’s kineticenergy?
Kinetic Energy Problem #1To stop the person, something has to do5915 J of work you might round 5915 J to 5900 to account for the two significant digitsIf the thing that does the work is thewindshield (how many of you don’t weara seat belt because “you’re just going upthe street?”), the stopping distancewould be about 3.0 cm (0.030 m).How much force would be applied to theperson’s skull?
Kinetic Energy Problem #1If instead of the windshield, theperson’s air bag did the work, whatwould the force on the person’sskull be? (air bags would increasethe stopping distance from 0.03 mto 0.3 m)
Kinetic Energy and Car CrashesThat’s still a lot of force, but it’s10x’s less than the windshield.Luckily, cars are equipped withother devices designed to absorbthe kinetic energy. seat belts crumple zones
Kinetic Energy Problem #2A total of 12,000 J of work is required tostop a 45 kg cart. a) what speed was the cart traveling before it was brought to a stop? b) if the cart was stopped over a distance of 3m, what was the magnitude of the force?
Finish the Warm-Up Quiz (Reg)4. Two eggs are thrown with equalvelocity. Egg #1 has a stoppingdistance of 0.5 meters and egg #2has a stopping distance of 1.0meters. Which egg has thegreatest force of impact?
Finish the Warm-Up Quiz (Reg)5. Jamie throws a baseball at a sheetand the ball pushes the sheet back 0.3meters.Jordan throws a baseball at a sheetand pushes it back 0.6 meters.Compare the kinetic energy Jamiegave the ball compared to the kineticenergy Jordan gave the ball. Be asspecific as you can.
Finish the Warm-Up Quiz (Hon)4. An egg is given 100 J of kineticenergy. It is brought to a stop overa distance of 2 meters. If theimpact force that will crack an eggis 60 N, does the egg shell break?Use mathematical fact to supportyour answer!
Finish the Warm-Up Quiz (Hon)5. A bowling ball has a mass of 7kg. It is rolled down a frictionlessbowling lane at a velocity of 10 m/s.It strikes one 2 kg bowling pinhead-on. If there is no back-stop,how far will the pin travel? Usemathematical fact to support youranswer!
Finish the Warm-Up Quiz (Hon ADV)6. A chicken egg has a mass of 60grams (0.06 kg). If it is droppedfrom a height of 0.8 m and createsa 2.5 cm dent in the flour, howmuch impact force was applied tothe egg? BE CAREFUL WITH YOURUNITS!!! Use mathematical fact tosupport your answer!