## Tuesday, April 29, 2014

### Tracker: valarylim student inleastic Collision of 2 marbles on a horizontal track

helping leongster to mentor students in becoming like scientists!

 http://weelookang.blogspot.sg/2014/04/tracker-inleastic-collision-of-2.html video by valary lim, kinematics model by lookang 1. explain why the model A is written as x = if(t<0.333,0.60*t,if(t>0.333,0.1998+0.15*(t-0.333),0)) 2. explain why model B is written as x = if(t<0.333,0.205,0.205+0.44*(t-0.333+0.0333)) https://www.dropbox.com/s/4ypouk5hgc69hww/304-307valarylimmarble_analysisandmodel.trz

## Mentoring Suggestions

hi valary lim,
good effort on the video tracking.
some points to note.
1. video taking need to firm on a mount to reduce error in movement

some physics ideas for you to think about.
1. show that momentum is conserved just before and just after collision in the TRZ file i uploaded?
2. from the kinetic energies of the 2 masses (assume to be same mass for both marbles) suggest what type of collision it is? ( elastic, inelastic or partial inelastic ?)

u can refer to Mr Wee's TRZ for reference and the model A and B built inside
model thinking questions:
1. explain why the model A is written as x = if(t<0.333,0.60*t,if(t>0.333,0.1998+0.15*(t-0.333),0))
2. explain why model B is written as x = if(t<0.333,0.205,0.205+0.44*(t-0.333+0.0333))

extension problem:
1. using the acceleration graphs to estimate the average impact-contact force on marble A and B and the highest instantaneous impact-contact force.

enjoy!

## Answer to explain the model A and B

1. model A is written as x = if(t<0.333,0.60*t,if(t>0.333,0.1998+0.15*(t-0.333),0))
the syntax for kinematic model is if ( variable < value , true do this, false to that )
so t is time, so if time is less than 0.333 seconds, the model is x = 0.60*t where 0.60 is the velocity
in the nested if loop, if time is greater than 0.333 seconds, x = 0.1998+0.15*(t-0.333) where 0.1998 is the initial x position,  0.15 is the velocity and (t-0.333) is needed to make the particle model appear only after 0.333.
else x = 0 which in this model which do nothing in particular since t < 0.333 and t > 0.333 covers all time or case.

2. explain why model B is written as x = if(t<0.333,0.205,0.205+0.44*(t-0.333+0.0333))
in the same manner, if time less than 0.333, do x = 0.205 (fixed position) else do x = 0.44*(t-0.333+0.0333) where 0.44 is the velocity of mass B