September 8th, 2008, 11:05 AM  #1 
Newbie Joined: Oct 2007 Posts: 7 Thanks: 0  A Ball is thrown into the air...
Here's the problem: Imagine throwing a rock straight up in the air. What is the initial velocity if the rock reaches a max height of 100m? There is no mention of time, which seems to be the only variable I need to solve the problem. What I have: A(t)=10 (to keep it simple) V(t)=10t+Vo here we have initial velocity. V(t) is 0, but we still can't determine Vo S(t)=100=5t^2 + Vot + CC is initial height (0m), When I solve for Vo in S(t) and substitute it in V(t), I get t=sqrt(20), with Vo=44.72, and the book says the answer is 80. Can someone help please? Thanks! 
September 8th, 2008, 02:44 PM  #2 
Senior Member Joined: May 2008 From: York, UK Posts: 1,300 Thanks: 0  Re: A Ball is thrown into the air...
If the question really is as you stated, I think you are right.

September 9th, 2008, 01:52 PM  #3 
Senior Member Joined: May 2007 Posts: 402 Thanks: 0  Re: A Ball is thrown into the air...
The total energy before throwing it and at it's peak must be the same. Here, I mean the kinetic and potential energy. So, you have: 
January 23rd, 2018, 12:55 PM  #4 
Newbie Joined: Jan 2018 From: Iowa Posts: 1 Thanks: 0 
The problem is 100 feet not meters, so you wouldn't use 9.8m but 16ft. You we're doing it right the whole time just with the wrong numbers.

January 23rd, 2018, 05:04 PM  #5  
Math Team Joined: Jul 2011 From: Texas Posts: 2,778 Thanks: 1429  Quote:
$v_f^2 = v_0^2  2g \cdot \Delta y$ at maximum height, $v_f = 0$ ... $0 = v_0^2  2g \cdot \Delta y \implies v_0 = \sqrt{2g \cdot \Delta y} = \sqrt{1960} \approx 44.4 \, m/s$  

Tags 
air, ball, thrown 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
If a ball is thrown...  Shamieh  Calculus  1  September 9th, 2013 10:57 AM 
Ball collision  one dropped and the other thrown up  PhizKid  Physics  1  September 19th, 2012 09:07 PM 
Can you find a 4 ball contained in a 3 ball, with not equal?  xinglongdada  Real Analysis  3  June 8th, 2012 12:13 AM 
identical balls are thrown randomly into bins  ozerdem  Algebra  4  February 21st, 2012 12:17 AM 
5 same red ball and 5 same white ball  cloudtifa  Advanced Statistics  0  October 18th, 2010 07:58 PM 