a. Calculate the buoyant force (in N) (upward) on a 2.00 L helium balloon. b. Given the mass of the rubber in the balloon is 1.30 g, what is the net vertical force (in N) (upward) on the balloon if it is let go? You can neglect the volume of the rubber.

a.

Given data:

Volume of helium balloon is, $V=2.00 \mathrm{L} =0.002 {\mathrm{m}}^3$.

The buoyant force is calculated as,

$F_b={\rho }_a\times g\times V$

Here, ${\rho }_a$ is the density of air, its value is $1.225 \mathrm{kg}/{\mathrm{m}}^3$ and g is gravitational acceleration, its value is $9.8 \mathrm{m}/{\mathrm{s}}^2$.

Solving as,

$$\begin{gathered} F_b={\rho }_a\times g\times V \\ {F}_b=1.225\times 9.8\times 0.002 \\ {F}_b=0.0240 \mathrm{N} \end{gathered}$$

Thus, required buoyant force is of 0.0240 N.

b.

Given data:

Mass of rubber in balloon is, $m=1.30 \mathrm{g}=1.3\times {10}^{-3} \mathrm{kg}$.

Net vertical force is given as,

$F_v=F_b-W_{He}-W_r .......................\left(1\right)$
Here, $W_{He}$ is the weight of helium and its value is calculated as,

$W_{He}={\rho }_{He}\times V\times g$

Here, ${\rho }_{He}$ is density of Helium, its value is $0.1785 \mathrm{kg}/{\mathrm{m}}^3$.