HPhys Unit 07 COEM Packet 2012

Name: ________________________________

Conservation of Energy ModelENERGY “Cheat”sheet

Symbol Type of Energy When is this energy present? Equation Notes

Honors Physics / Unit 07 / COEM

– 1 – from Modeling Workshop Project © 2006

Spring Force vs. Displacement (Stretch)

200 2 4 6 8 10 12 14 16 18

1.6

0

0.2

0.4

0.6

0.8

1

1.2

1.4

!x (cm)

Fs (

N)

Spring 1: k = 0.034 N/cm

200 2 4 6 8 10 12 14 16 18

1.6

0

0.2

0.4

0.6

0.8

1

1.2

1.4

!x (cm)

Fs (

N)

Sprin

g 2: k

= 0

.069 N

/cm

!

200 2 4 6 8 10 12 14 16 18

1.6

0

0.2

0.4

0.6

0.8

1

1.2

1.4

!x (cm)

Fs (

N)

Sprin

g 2: k

= 0

.069 N

/cm

Spring 1: k = 0.034 N/cm


from Modeling Workshop Project © 2006 ! – 2 –

Worksheet 1: Energy Pie ChartsINSTRUCTIONS: Use pie charts to analyze the energy changes in each situation given.• Designate your choice of system by explicitly listing the objects included.• Divide the pies in a qualitatively accurate fashion, and label them with the energy storage

mechanism involved.

1. A ball is held above the ground, and then is dropped so it falls straight down.! (Restrict your analysis to the ball moving in the air, BEFORE it hits the ground.)

List the objects in your system Draw a pie chart for each positionDraw a pie chart for each positionDraw a pie chart for each position


2. A wind-up toy is wound up, then "walks" across a table and comes to a stop.

!




3. An object rests on a coiled spring, and is then launched upwards.

List the objects in your system

Draw a pie chart for each position

!

4. A piece of clay is dropped to the floor.

List the objects in your system

Draw a pie chart for each position

5. A truck is driven at constant speed down the street.




Worksheet 2: Springs and Energy

6. Suppose in the spring lab, one group found that Fspring = (1000 N/m)(∆x). Construct a graphical representation of force-vs-displacement. (Hint: make the maximum displacement 0.25 m.)

Graphically determine the amount of energy stored while stretching the spring from x = 0 cm to x = 10 cm.

Graphically determine the amount of energy stored while stretching the spring from x = 15 cm to x = 25 cm.

7. The graph below was made from data collected during an investigation of the relationship between the amount two different springs stretched when different forces were applied.

For each spring, determine the spring constant.

For each spring, find the amount of force required to stretch the spring 3.0 m.

For each spring, find the Us stored when stretched 3.0 m.

Determine the amount that Spring A needs to be stretched in order to store 24 joules of energy.

!

�

�

�

�

�

�

�

�

�

�

�

�

�

�

�

Spring A

Spring B

1 2 3 4 5 6 7 8x �m �

5

10

15

20

25

30

35

40F �N�



Worksheet 3: LOL Diagrams

8. A car on a frictionless roller coaster track, launched by a huge spring, makes it to the top of the loop.

Energy FlowDiagramK UsUg K Ug Us !Etherm

Initial FinalInitial Final

vv=0

Qualitative conservation equation:

9. Same as problem 8, but with the spring outside of the system.



vv=0


10. Same as problem 8, but with friction between the cart and the track.



vv=0




11. Same as problem 8, but we take our final snapshot earlier this time (the cart is only half-way up the loop).



vv=0


12. A moving car, moving up a hill, coasts to a stop up.



v

v=0


13. A person pushes a stalled car to get it to the service station.



vv=0




14. A load of bricks, resting on a compressed spring, is launched into the air.



v

v=0 y=0


15. Same as problem 14, but with the spring outside of the system.



v

v=0 y=0


16. Superman, stopping a speeding locomotive, is pushed backwards a few meters in the process.

Initial Final

v v=0


Initial Final




17. A moving block hits a spring, traveling at 5 m/s at the time of contact. At the instant the block is motionless, by how much is the spring compressed? Assume none of the initial energy ends up stored as thermal energy.



v=5.0 m/s v=0

m=8.0 kg k=50 N/m


18. Determine final velocity of the cart, assuming that 10% of the initial energy ends up stored as thermal energy due to the friction between the cart and the road.



v=?

v=0

m=20 kg

0

5m




Worksheet 4: Problem Solving

19. Your cousin Throckmorton pulls a 50 kg box with a force of 100 N. The coefficient of kinetic friction is 0.15. The box starts with a speed of 1.2 m/s and moves 6 meters before you get bored watching your cousin pull a box.

!



20. A 24 kg child descends a 5.0 m high slide and reaches the ground with a speed of 2.8 m/s.

21. A chunk of rock of mass 50.0 kg slides down the side of a volcano that slopes up at an angle of 30.0º to the horizontal. If the rock accelerates at a rate of 3.0 m/s2, what is the coefficient of kinetic friction between the rock and the side of the volcano?



22. A man stands on the roof of a building that is 30.0 m tall and throws a rock with a velocity of magnitude 40.0 m/s at an angle of 33.0 degrees above the horizontal. Air resistance may be ignored.



23. A 0.500 kg block attached to a spring with length 0.60 m and spring constant 40 N/m is at rest with the back of the block at point A on a very low-friction, horizontal table. You pull the block to the right along the surface with a constant horizontal force of 20 N. When the back of the block reaches point B, you let go of the block.



24. A 2.00 kg package is released from rest on a 53.1º incline, 4.00 m from a long spring with a 140 N/m spring constant that is attached at the bottom of the incline. The coefficients of friction between the package and the incline are µs = 0.40 and µk = 0.20.



25. In a physics lab experiment, a spring clamped to the table shoots a 20 g ball horizontally. When the spring is compressed 20 cm, the ball travels horizontally 5.0 m and lands on the floor 1.5 meters below the point at which it left the spring.



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HPhys Unit 07 COEM Packet 2012

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