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Grade: 11
        
Suppose the coefficient of friction between an athlete's shoes and the ground is 0.9. The athlete starts running with an acceleration a. Then the equation will be ma=mμ. This equation means that the body is in equilibrium but according to the question the athlete is running. How is this possible?
one month ago

Answers : (3)

Arun
22331 Points
							
To reach the minimum time he has to move with maximum possible acceleration.
Let the maximum acceleration be a.
ma-μR=0
ma=μmg
a=μg=0.9x10=9 m/s2
A) Initial velocity=u= o m/s
t=?
a=9m/s2 
s=5m
From s= ut +1/2 at²
50=0+1/2 at²
t=100/9
t=10/3 sec=3.3 sec
b) AFTER MOVING 50m, velocity of the athelete given by :
V=u+at=0+9x 10/3
he has to stop in minimum time, so deceleration is 
-a=-9 m/s2 
R=mg
ma=μR
a=μg =9m/s2[deceleration]
u1=30m/s
v1=0 m/s]t=v1-u1/a
t=0-30/-a
t=-30/-9
t=10/3 sec=3.3 sec

 
 
one month ago
Vikas TU
8447 Points
							
Hiii 
The force that the ground can exert on man is equal and opposite to the force of friction on the ground. 
There is misconceptions in this . 
That does not mean man should be at rest . 
one month ago
Khimraj
3008 Points
							
AFTER MOVING 50m, velocity of the athelete given by :
V=u+at=0+9x 10/3
he has to stop in minimum time, so deceleration is 
-a=-9 m/s2 
R=mg
ma=μR
a=μg =9m/s2[deceleration]
u1=30m/s
v1=0 m/s]t=v1-u1/a
t=0-30/-a
t=-30/-9
t=10/3 sec=3.3 sec
 
one month ago
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