March 31st, 2017, 03:34 AM  #1 
Member Joined: Mar 2017 From: Tasmania Posts: 36 Thanks: 2  now enough info
A tennis ball traveling at 20ms/s southeast hits a wall and bounces back at a velocity of 16ms/s southwest. Listing any assumptions you make, estimate a the inital momentum of the ball b the change in momentum of the ball I get how to calculate inital momentum and change in momentum but I just do not think enough information is given for the question I must be missing something help plz 
March 31st, 2017, 04:17 AM  #2 
Senior Member Joined: Feb 2016 From: Australia Posts: 1,476 Thanks: 495 Math Focus: Yet to find out. 
You are correct, there isn't enough information given. But the question also asks to list your assumptions, so it's up to you to come up with some reasonable assumptions. My assumptions would be for the directions the ball travels. Draw your set of axis. South east would 45 degrees from the positive horizontal axis, similarly, south west would be 135 degrees from the positive horizontal axis (45 from negative horizontal axis). 
March 31st, 2017, 05:22 AM  #3 
Member Joined: Mar 2017 From: Tasmania Posts: 36 Thanks: 2 
Does that also mean give the tennis ball a mass?

March 31st, 2017, 05:26 AM  #4 
Senior Member Joined: Feb 2016 From: Australia Posts: 1,476 Thanks: 495 Math Focus: Yet to find out. 
Not necessarily. Try solve symbolically first. Things tend to cancel out.

March 31st, 2017, 07:08 AM  #5 
Math Team Joined: Jul 2011 From: Texas Posts: 2,692 Thanks: 1351  
March 31st, 2017, 04:48 PM  #6 
Member Joined: Mar 2017 From: Tasmania Posts: 36 Thanks: 2 
Isn't momentum defined as p = mv? I'm still a little confused, sorry.
Last edited by skipjack; April 1st, 2017 at 09:06 AM. 
March 31st, 2017, 05:38 PM  #7  
Math Team Joined: Jul 2011 From: Texas Posts: 2,692 Thanks: 1351  Quote:
$\vec{p} = m\vec{v}$ Last edited by skipjack; April 1st, 2017 at 09:07 AM.  
April 1st, 2017, 06:26 AM  #8 
Member Joined: Mar 2017 From: Tasmania Posts: 36 Thanks: 2 
So how am I meant to figure out p0 if I'm only given velocity? I must be missing something from your diagram.
Last edited by skipjack; April 1st, 2017 at 09:05 AM. 
April 1st, 2017, 08:47 AM  #9  
Math Team Joined: Jul 2011 From: Texas Posts: 2,692 Thanks: 1351 
$p_0 = 20m$, where $m$ is the mass of the tennis ball ... Quote:
 
April 1st, 2017, 08:28 PM  #10 
Member Joined: Mar 2017 From: Tasmania Posts: 36 Thanks: 2 
I believe that this question is rather debatable as the weight has not been given would I be right in assuming this


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