The net force (\(F_{\text{net}}\)) is the weight (\(W\)) minus the total upward forces (upthrust (\(U\)) and viscous drag (\(F_{\text{drag}}\))), and this net force causes the acceleration (\(a\)) according to Newton's second law (\(F_{\text{net}}=ma\)):

\(F_{\text{net}} = W - U - F_{\text{drag}}\)

\(ma = (m \times g) - U - F_{\text{drag}}\)

\((10\text{ kg}) \times a = (10\text{ kg} \times 10\text{ m/s}^{2}) - 10\text{ N} - 15\text{ N}\)

\(10a = 100\text{ N} - 25\text{ N}\)

\(10a = 75\text{ N}\)

\(a = \frac{75\text{ N}}{10\text{ kg}}\)

\(a = 7.5\text{ m/s}^{2}\).