Calculating Work Done by Upward Buoyant Force on Hot Air Balloon

[azhang40]

Homework Statement

A hot air balloon of mass 425 kg ascends from the ground level and accelerates at a rate of 1.25 m/s/s for 25 seconds. How much work is done by the upward buoyant force on the balloon?

(conceptual) A certain amount of work W is required to accelerate a car from rest to a speed of v. How much work is required to accelerate from rest to a speed of v/2?

Homework Equations

W=fd
Fnet=ma
KE=1/2mv^2

The Attempt at a Solution

I tried to find Fnet first, so would it be the upward buoyant force (what is trying to be solved)+mg (weight)= 425x1.25. Then find the displacement using one dimensional motion, getting 390.625 m traveled. Is all this right? How do I proceed?

Rearranged W=1/2m(v/2)^2 to 4w=1/2mv^2. How do I proceed? I'm solving for work required.

 

[jedishrfu]

Cant you simply compute the height the balloon reached and then use PE=mgh ?