physics
posted by karim .
A hotair balloon of mass 200 kg is descending vertically with downward acceleration of magnitude 1.2 m/s2. How much mass (ballast) must be thrown out to give the balloon an upward acceleration of magnitude 1.2 m/s2 (same magnitude but opposite direction)? Assume that the upward force from the air (the lift) does not change because of the decrease in mass.

Let B = the buoyancy force and M = the initial total mass. Let m be the ballast mass released
M g  B = M*1.2 m/s^2
(Mm)g B = M*1.2 m/s^2
Solve for m.
m g = M*2.4m/s^2
m/M = 2.4/g
m = 0.245 M = 49 kg