The gravitational potential energy \( U \) is calculated using the formula \( U = mgh \). Given \( m = 5 \, \text{kg} \), \( g = 9.8 \, \text{m/s}^2 \), and \( h = 10 \, \text{m} \), the substitution yields \( U = 5 \times 9.8 \times 10 \), resulting in \( U = 490 \, \text{J} \). Therefore, the object's gravitational potential energy is \( 490 \, \text{J} \).