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A physics problem

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HKizzle
Posts: 401 - Karma: 19
Cab anybody tell me how to solve this?
A German V2 rocket from WW2 had a range of 300km, reaching a maximum height of 100km. What is the rocket's maximum initial velocity?
Oct 4 2010 3:35PM
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Indoobly
Posts: 125 - Karma: 14
im sure you would need more information for that, like the time it takes to cover that distance so you can do speed=distance/time
Oct 4 2010 3:58PM
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Tasche
Posts: 5422 - Karma: 99
Can't really answer this one with the information given.

You need to give flight time and some other info because a rocket unlike a bullet has a force on it the entire time and not just an initial launch force.

Also maximum initial velocity makes no sense because the initial velocity should be 0 because it is sitting on the ground and the maximum velocity would just be the next instant after the motor is lit...
Oct 4 2010 3:59PM
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COskier
Posts: 1066 - Karma: 131
^You can answer it easily.

Equations of motion dude.
Oct 4 2010 4:00PM
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Tasche
Posts: 5422 - Karma: 99
with a projectile ya, but not a powered rocket.
Oct 4 2010 4:00PM
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ataraxia
Posts: 903 - Karma: 117
The rocket has travelled 150km at its max height of 100km. It vertical velocity component is equal to 0 at this point. solve for the initial velocity (y component) using, v^2=v(initial)^2 + 2(g)(y). With this value solve for the time of the whole trajectory. Then find out the initial x component. Add the x and y vectors together and solve the angle using tan(theta) = y component/ x component.
Oct 4 2010 4:07PM
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word-sauce
Posts: 1151 - Karma: 11

you use a system of equations and solve for vi which is v initial

1: dy=vi1/2T+1/2aT             the first 1/2 T is because your using a height of 100 which is half way through the parabolic motion, a is gravity or 9.81

2.dx=viT        there is no 1/2at^2 because a=0 in the x direction

now you simply solve this system for vi the t's should cancel out

Oct 4 2010 4:07PM
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COskier
Posts: 1066 - Karma: 131
I guess thats true, but obviously the prof is talking about a projectile situation here, so I'd say 4430 m/sec.
Oct 4 2010 4:07PM
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HKizzle
Posts: 401 - Karma: 19
We're treating the rocket as a projectile in this case.
Oct 4 2010 4:07PM
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word-sauce
Posts: 1151 - Karma: 11
^ nvm i like his better
Oct 4 2010 4:08PM
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HKizzle
Posts: 401 - Karma: 19
haha thanks, +k for all
Oct 4 2010 5:08PM
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I_Am_Mod
Posts: 13214 - Karma: 3,753
newschoolrs is so epicwhenn you're drunk, i'll answer dis tomorrow !

cheers, luv u all !
I <3 NS
Oct 4 2010 5:33PM
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