Lab: Momentum.

Essay by eviiil October 2005

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To find out whether momentum and kinetic energy are conserved.


Theoretically momentum should be conserved at all times whereas energy is lost if the collision is not a fully elastic one through heat and sound.


The Independent variable is the initial and final mass of the trolley. The Dependent variable is the velocity of the trolley.


i) Set up apparatus as shown in the diagram.

ii) Start ticker timer and give the trolley a brisk push.

iii) Drop a book from your hands onto the trolley as it runs beneath.

iv) Run off enough tapes for each member of your group.

v) Measure the mass of your book and the trolley.


mtrolley = 805g ± 10g

mbook = 845g ± 10g

Ticker timer goes at 50Hz = 1/50s = 0.02s

vi = di / Δt vf = d2 / Δt

di = 5.4cm ± 0.1cm

vi = 0.54ms-1

d2 = 1.8cm ± 0.1cm vf = 0.18ms-1

Ek = mv2 / 2

Ek before = 0.117369 J

Ek after = 0.02673 J

Pbefore = Pafter

Pbefore = mv Pbefore = 0.4347 kgms-1

Pafter = (m + m)v Pafter = 0.297 kgms-1

Evaluation and Analysis:

The obtained results don't support my hypothesis since they show that neither energy nor momentum is conserved in this situation. The momentum after the collision decreased by a factor of approx. 1.5 whereas kinetic energy has decreased by almost a factor of 4.5. Due to friction from the table and the ticker timer the measurements taken were not 100% accurate. Friction was the main cause of inaccuracy in this experiment.

Kinetic energy is lost in this experiment and has been transformed into heat and sound.

Another factor contributing to inaccuracy is that the book was dropped by a person and humans tend...