Question 6: In the relation $\mathrm{F}=\mathrm{G}\frac{Mm}{d^2}$, the quantity G

Usain, a talented sprinter, participates in a 800 meter race. He starts from rest and for the 

first 200 m accelerates uniformly to reach a maximum speed of 20 m/s. However, during the 

race, in the next 100 m he moves with constant speed. He slows down due to a muscle cramp 

and comes to a stop just 400 meters from the starting line.

Answer the following: 

a) Calculate Usain's acceleration during the initial part of the race. 

b) Calculate the acceleration during the next part of the race.

c) Determine the time taken by Usain to reach his maximum speed.

 OR

c) How much time he could take to complete the race if he would not have muscles cramp

and moved with the same acceleration