Question

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 =

Answer 1

Answer:

(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 $KE_i=\frac{1}{2}mv^2=\frac{1}{2}\times 65.5\times 4.20^2=577.71J$

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

Now kinetic energy is $KE_f=\frac{1}{2}mv^2=\frac{1}{2}\times 65.5\times 8.40^2=2310.84j$

So the factor by which kinetic energy will change $=\frac{KE_F}{KE_I}=\frac{2310.84}{577.7}=4$