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

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

## Homework Statement

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?

F=ma

## 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

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rock.freak667
Homework Helper

Resultant force= Upward force-downward force

what's the downward force in this case?

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

rock.freak667
Homework Helper

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

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
Homework Helper

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
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?

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

rock.freak667
Homework Helper

we have the distance(1.50) and we now have an acceleration but would vinitial still be equal to zero??
Yes it would be safe to assume the initial velocity as zero.

thank you so much