World-class sprinters can accelerate out of the starting blocks with an acceleration that is nearly horizontal and has magnitude 15m/s2. 1) How much horizontal force F must a sprinter of mass 51kg exert on the starting blocks to produce this acceleration?

World-class sprinters can accelerate out of the starting blocks with an acceleration that is nearly horizontal and has magnitude 15m/s2.
1) How much horizontal force
F must a sprinter of mass 51kg exert on the starting blocks to produce this acceleration?
2) Which body exerts the force that propels the sprinter, the blocks or the sprinter?
A particle is moving along a straight line with the acceleration a (12t-3t^1/2)ft/s^2 where t is in seconds. Determine the velocity of the particle as a function of time. When t=0,v=0 , and s= 15 .
A tennis ball is given horizontal velocity of 8 m/s when it is hit at a height of 1.8 m above the ground. It is in air for how many seconds?