Unit 07“Work, Power, Energy

and Energy Conservation”

LabPredicting the Final Velocity of a Car

Using the Conservation of Mechanical Energy

Background Information•What variable(s) can be calculated to help determine this?

•Which equation(s) can be used for solve for the calculated variables?

•What variable(s) are known?

•What variable(s) can be measured? How?

Background InformationOther important information:

Background Information

PEi =mghi

KEi = 0

PEf =mghf

KEf = ½mv2

•What variable(s) can be calculated to help determine this?

•Which equation(s) can be used for solve for the calculated variables?

•What variable(s) are known?

•What variable(s) can be measured? How?

Final Velocity (Vf)Total Mechanical Energy (ME)

MEi = MEf

ME = PE + KE

Vi = 0m/sg = 9.8m/s2

Δxflag = 0.01m

hi measure with meter stickhf measure with meter stickVf measure time (Δtsensor) with sensor to get velocity

PE =mghKE = ½mv2 V = Δxflag/Δtsenor

Background InformationOther important information:

•The Law of the Conservation of Mechanical Energy: Total Mechanical Energy must stay the same unless there is friction.

•The Law of the Conservation of Energy: Energy cannot be created or destroyed. Only converted from one form to another.

•Kinetic Energy: Energy of Motion•Potential Energy: Energy of Position

Procedure:Part I:1.Obtain an inclined plane set up, and car. 2.Set up the sensor at point between the top and bottom points (as indicated in class).3.Place the car at the top of the track, measure the initial height of the car. 4.Record this data (in meters) in the data table (hinitial).5.Measure the final height of the car (at the second sensor).6.Record this data (in meters) in the data table (hfinal).7.Use data to calculate initial mechanical energy and predict the final velocity of the car.

• mcar=0.057kgPart II:1.Be sure the cord is plugged into the Part A of the sensor, press “A” and “interval” on sensor.

• Green lights on!2.Place car at the top of the track (where you measured the initial height).3.When ready, release the car.4.Record the time from the sensor at the bottom of the track.

• Δx=0.01m, the width of the flag5.Using data to calculate the final velocity of the car. 6.Compare the predicted and experimental final velocity of the car.

Data & Calculations Table:Part I “Predicted Final Velocity”:

Initial Height

(m)hinitial

Initial Potential Energy

(J)PEi

Initial Kinetic Energy

(J)KEi

Initial Total Mechanical Energy

(J)MEi

    

   

 

Final Height

(m)hfinal

Final Potential Energy

(J) PEf

Predicted Final Kinetic Energy

(J)KEf

Predicted Final Velocity

(m/s)Vf

       

 

Data & Calculations Table:Part II “Actual Final Velocity”:

SensorTime

(s)Δt

Actual Final Velocity (m/s)

Vf experimental

Percent Error

(%)

Calculations - Part I:

1. Use the equation MEinitial=MEfinal to predict the final velocity of the car.

Calculations Part II:

1. Final Velocity: Vf=Δx/Δt

2. Percent Error: %Error = (Vf actual – Vf predicted) x 100

Vf predicted

Conclusion Question:1.Did your predicted final velocity match your actual final velocity? Use the Law of the Conservation of Mechanical Energy to explain. Use data to support your answer.(A.E.S.)  

2.Is the total energy conserved in this lab? Use the Law of the Conservation of Energy to explain why or why not. (A.E.S.)