Solutions: 620 N
To solve this question, you need to apply conservation of energy (COE) to find the kinetic energy (KE) that the boy possesses just before he reaches the ground.
After which, you can solve the question using (1) Conservation of energy or (2) Kinematics to solve.
Using COE to find the KE just before he reaches the ground.
Method 1: Using Conservation of Energy (COE)
Method 2: Using Kinematics
You must know these 2 methods and always think along this 2 directions when dealing with such questions.