An athlete with a mass of 65.5 kg is in a cross country race, and at one instant he has a speed of 4.20 m/s. (a) what is his kinetic energy at this instant? kei = j (b) if he wishes to doubles his speed to reach the finish line, his kinetic energy will change by what factor? kef kei =

(A) Kinetic energy will be 577.7 j

(b) Factor by which kinetic energy will change is 4                      

Explanation:

We have given mass of the athlete m = 65.5 kg

He has a speed of 4.20 m/sec

So v = 4.20 m/sec

(a) Kinetic energy is given by

(B) Now he wishes to doubles his speed So now speed = 4.20×2 = 8.40 m/sec

Now kinetic energy is

So the factor by which kinetic energy will change

i am pretty sure it is c because when people are closer together, they cannot move as freely. picture being in a mostly full elevator, for instance. the people are right next to you, and you can barely move.