Answer:
(a) The horizontal ground reaction force 
(b) The vertical ground reaction force 
(c) The resultant ground reaction force 
Explanation:
Given
John mass , m = 65 kg
Horizontal acceleration , 
Vertical acceleration , 
(a) Using Newton's 2nd law in horizontal direction

=>
Thus the horizontal ground reaction force 
(b) Using Newton's 2nd law in vertical direction

=>
=>
Thus the vertical ground reaction force 
(c) Resultant ground reaction force is

=>
=>
Thus the resultant ground reaction force 
Let t=time to reach the ground=8 secs, g= acceleration of gravity. The speed v on reaching the ground is gt=8g=78.4 m/s where g=9.8 m/s/s approx.
Answer:
9. The Sun's Gravity
10. The core is the densest layer