# Final velocity of a ball pushed by compressed airpls. help

1. May 18, 2009

### brunettegurl

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

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

2. May 18, 2009

### rock.freak667

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

Resultant force= Upward force-downward force

what's the downward force in this case?

3. May 18, 2009

### brunettegurl

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

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

4. May 18, 2009

### rock.freak667

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

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)

5. May 18, 2009

### brunettegurl

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

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

6. May 18, 2009

### rock.freak667

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

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

and in the formula $v_1^2=v_0^2+2ad$

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

7. May 18, 2009

### brunettegurl

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

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

8. May 18, 2009

### rock.freak667

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

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

9. May 18, 2009

### brunettegurl

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

thank you so much

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