final velocity of a ball pushed by compressed air..pls. help!!

brunettegurl

1. The problem statement, all variables and given/known data
Compressed air is used to fire a 1.72 kg ball vertically upward from a 1.50 m long
tube. The air exerts a upward force of 28.7 N on the ball as long as it is in the tube.
With what velocity does the ball leave the top of the tube?


2. Relevant equations
F=ma
V₁² = v₀²+2ad


3. The attempt at a solution
so i used the given mass and force to get an acceleration. then using the acceleration i plugged it in to the second equation assuming vinitial to be zero and my asnwer is coming out wrong can someone point me in the right direction thanx :))

rock.freak667

Resultant force= Upward force-downward force

what's the downward force in this case?

brunettegurl

wld the downward force be the friction..but there is no mention of any friction in the question

rock.freak667

if you throw a ball upwards, it does not continue to go upwards, what makes it fall back to earth? (it has a mass m and is under the influence of gravity g)

brunettegurl

ok but that tells us what happens after it is released they're asking for velocity just before it's released from the cannon/tube

rock.freak667

When you find the resultant force, you can get the resultant acceleration...

and in the formula [itex]v_1^2=v_0^2+2ad[/itex]

what do you need to find to get the value for v₁?

brunettegurl

we have the distance(1.50) and we now have an acceleration but would vinitial still be equal to zero??

rock.freak667

Yes it would be safe to assume the initial velocity as zero.

brunettegurl

thank you so much :))