Answer: The blocks
Explanation:
When the sprinter takes off, he/she presses hard on the block.
The blocks apply an equal and opposite force to the sprinter according to Newton's 3rd law of motion.
The reaction force from the blocks gives the sprinter the initial acceleration to begin the race.
Answer: 21965.517 Pa
Explanation:
Pressure 
is the force 
exerted by a gas, a liquid or a solid on a surface (or area) 
, its unit is Pascal 
which is equal to 
and its formula is:
(1)
In this case we have the surface of a sole of a tennis shoe:
(2)
And the mass 
of the person who wears it:
On the other hand, we know the weight is the force the Earth exerts on people and objects due gravity 
:
(3)
Substituting (2) and (3) in (1):
(4)
Finally:
This is the pressure the shoe exert on the ground
