Question

The US athlete Florence Griffith Joyner won the 100 m sprint gold medal at Seol Olympic 1988 setting a new Olympic record of 10.54 s. Assume that she achieved her maximum speed in a very short time and then ran the race with that speed till she crossed the line. Take her mass to be 50 kg. (a) Calculate the kinetic energy of Griffith Joyner at her full speed. (b) Assume that the track, the wind etc. offered an average resistance of 1/10th of her weight, calculate the work done by the resistance during the run. (c) What power Griffith Joyner had to exert to maintain uniform speed ?
Concept of Physics - 1 , HC VERMA , Chapter " Work and Energy"

Answer 1

Here in the question :-
Given Mass m :- 50 kg.
Uniform speed of athlete v = d/t
= 100 m / 10.54 s
v = 9.49 m/s.

(a) K.E of the athlete @ full speed :- 1/2 mv²
= 1/2 ( 50× 9.49² )
= 4503.005 /2
= 2251 J.
K.E of the athlete at full speed is 2251 J. 


(b) Work done by resistance :-
Weight of the athlete = mg
= 50 × 9.8
=490 N.
 Now resistance force or force of the resistance ,
F = mg / 10
F = 49 N.
Since she is running with the constant speed, Net force occurring in the direction of movement is zero.
Now work done by the resistance,
= F ×s
= 49 × (-100 )    { Negative sign shows, It's opposite to the force}
= - 4900 J.
Hence work done by resistance is -4900 N.


(c) Power to maintain uniform speed :-
Her force applied is 49 N and constant speed is 9.49 m/s , then
Power = F × v 
P = 49 × 9.49
P = 465 W.

Hence power to maintain uniform speed is 465 W.




Hope it Helps.

Answer 2

Answer:

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