## College Physics (4th Edition)

$A_0=4\pi r_0^2$ After the balloon expands, the new surface area A is $2.0 \times A_0$. $A = 2.0 \times A_0$ $4 \pi r^2 = 2.0 \times 4 \pi r_0^2$ $r^2 = 2.0 \times r_0^2$ $r = \sqrt{2.0 \times r_0^2}$ $r = 1.4 \times r_0$ The radius increases by a factor of 1.4