Physics Help Forum Mastering Physics question

 Kinematics and Dynamics Kinematics and Dynamics Physics Help Forum

 Sep 7th 2009, 07:43 PM #1 Junior Member   Join Date: Apr 2009 Posts: 20 Mastering Physics question A 200 kg weather rocket is loaded with 100 kg of fuel and fired straight up. It accelerates upward at 33 m/s^2 for 32 seconds , then runs out of fuel. Ignore any air resistance effects. a) what is the rocket's maximum altitude? b) how long is the rocket in the air? I think the part that confuses me is the mass, if you could help me with this question that would be greatly appreciated.
 Sep 7th 2009, 07:58 PM #2 Physics Team     Join Date: Jul 2009 Posts: 310 Ignore the mass and continue the question like regular. __________________ "Dissent is the highest form of patriotism." - Thomas Jefferson. "Give me control of a nation's money and I care not who makes her laws." -Mayer Amschel Rothschild I study Mathematical Physics at the University of Waterloo. -DC
 Sep 26th 2009, 07:25 PM #3 Junior Member   Join Date: Apr 2009 Posts: 20 How do you determine the acceleration for this question though?
 Sep 27th 2009, 03:04 AM #4 Banned   Join Date: Aug 2009 Location: UK Posts: 240 Solidsnake, You have already asked a similar question to this on the 5/9/09 called Mastering Physics practice question. I know this because i made a complete mess of it myself until physicsquest came along, i understand the equation now. (Thanks to physicsquest) u=initial velocity v=final velocity t=time a=acceleration s=displacement to find the altitude (s) you first need to find the velocity (v), v= u + at u=0 , a=33m/s^2 , t=32, v=0+ 33 x 32 = 1056 m/s displacement (s) after fuel runs out = v^2 = 0= u^2 - 2as (a= being gravity, 9.8) 1056^2 = 1115136 (take into account that v becomes u) 1115136-1115136 = v^2, (v^2 in this case will be 0) 1115136/(2a) = s s= 56894.69 m, after fuel runs out t = s/((u+v)/2) t= 56894.69/((1056+0)/2) = 107.755 secs, after fuel runs out I'll leave you to find the rest, you still need to find (t) & (s) when the rocket had fuel and like Deco stated mass is irrelevant if your given (a) & (t), so you only need to find (s). Last edited by Paul46; Sep 27th 2009 at 07:56 AM. Reason: spelling