I added individual steps for clarity. Note that g must be positive if the solution is to be real.

Let me know if you have any questions.
Feeling of Weight.
When walking, you feel the weight on your feet, therefore, your brain automatically refers to it as a source of weight.
In the air there is no platform to land on, therefore the brain does not have the conscience to register you getting pulled down.
Kinetic energy.
Kinetic energy is the type of energy observed in moving objects. In this case the football player is running, ie moving, so he/she must have kinetic energy.
2,450 Joules, kinetic energy is 1/2 mass x velocity squared.
Answer: the most potential energy == 5 kg book, 2 m from the ground= 98 Joules
Explanation:
potential energy = m g h
m = mass
g = acceleration due gravity = 9.8 m/s²
h = distance above ground
1. Pe₁ = 1 kg x 2 m x g = 2 g
2. Pe₂ = 5 kg x 2 m x g = 10 g = 10 kg m x 9,8 m/s² = 98 Joules
3. Pe₃ = 1 kg x 0,5 m x g = 0,5 g
4. Pe₄ = 5 kg x 0.5 m x g = 2,5 g
10 > 2,5 > 2 >0,5