Answer:
External force on him will be 112 N
Explanation:
We have given the mass of the sprinter m =70 kg
Acceleration of the sprinter 
We have to find the net external force
According to second law of motion force = mass ×acceleration
Force is dependent on the mass and acceleration
So 
So external force will be 112 N
car starts from rest

final speed attained by the car is

acceleration of the car will be

now the time to reach this final speed will be



so it required 1.39 s to reach this final speed
They are called stem cells. This cells are undifferentiated which means it can specialize in other types when it receives the right stimuli. They can divide through mitoses and become more stem cell or become a bone, muscle, blood cell, etc.
They can have 2 origins: embryos or some human tissue; their function is to regenerate or substitute damaged cells
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Assuming that there were no encumbrances during it's foreswing and it reached it's full potential at apogee.