Final answer:
The buoyant force on a helium balloon can be calculated using the formula: Buoyant force = Weight of the fluid displaced. The net vertical force on the balloon when it is let go is the difference between the buoyant force and the weight of the rubber.
Step-by-step explanation:
(a) The buoyant force on a helium balloon can be calculated using the formula:
Buoyant force = Weight of the fluid displaced
Since helium is less dense than air, the buoyant force is equal to the weight of the air displaced by the balloon. The weight of the air can be calculated using its density and the volume of the balloon. The buoyant force is then given by:
Buoyant force = Density of air x Volume of balloon x Acceleration due to gravity
Substituting the values for the density of air, volume of the balloon, and acceleration due to gravity, we can calculate the buoyant force.
(b) The net vertical force on the balloon when it is let go is the difference between the buoyant force and the weight of the rubber. Since the mass of the rubber is given, we can calculate its weight using the formula:
Weight of an object = mass x Acceleration due to gravity
The net vertical force is then the difference between the buoyant force and the weight of the rubber.