How Is the Initial Upward Acceleration of a Weather Balloon Calculated?

[matt_crouch]

Homework Statement

assume the balloon is a spherical shape whose radius is 2.5m and total mass of 15 kg

a) what is the initial upward acceleration of the balloon when it is released from sea level

Homework Equations

The Attempt at a Solution

i know the volume of a sphere is =4/3 (pi)r³
so can calculate the volume
i know the density of the balloon is

p=m/v
and that the buoyancy is going to be greater than the weight
i reaaranged the equation and substituted m=pv into f_b=ma

to get f_b=pva

but i don't think this is the right way to do it
where am i going wrong and how do i finish the equation?

cheers

 

[matt_crouch]

please?

 

[kelsif]

i had a similar problem i solved for the force then the volume and manipulated the equation to read a=f/pv i got a reasonable answer

 

[matt_crouch]

ye i got the answer in the end. the acceleration comes out as about 42 m/s^2 but the next part of the question was to find where it reaches terminal velocity and it reaches it at 3m/s^2