Question

A balloon of total mass 1000kg float motionless over the earth's surface. if 100kg of sand ballast are thrown over board, the balloon starts to rise with an acceleration of?

Answer 1

Total Buoyancy force on the ballon = 1000 kg * g = 1000 kg wt
   (kg wt  means  multiply with  g to get Newtons)

After removing the 100 kg mass from the balloon, the weight 
   = 900 kg * g = 900 kg wt

Net force upwards :  100 kg wt
Net acceleration upwards = 100 kg wt / (1000 kg) = g / 10
   = 9.81/10 = 0.981 m/s²

Answer 2

Answer:

1.09m/s2

Explanation:

initially, the weight of the balloon is balanced by the upward thrust of air.

hence lets consider the upward thrust to be T.

T=mg

T=1000*9.8

=9800N

In the secon case since some weight is unloaded , the resultant weight now is only 900kg

hence, as the above an upward thrust acts on the balloon.

but now,

the baloon rises with an aceeleration of, say, a

so T=mg-ma

9800=900(9.8)-900a

solve for "a"

we get it as 1.09m/s2