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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?
11 months ago

Answers : (5)

Arun
24716 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

 
 
11 months ago
Vikas TU
11655 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 . 
11 months ago
Khimraj
3007 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
 
10 months ago
aswanth nayak
100 Points
							
Dear student,
                         
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
 
 
hope this helps you
7 months ago
Mahesh Koilada
22 Points
							
According to Newton’s 2nd law, the net of external forces acting on a body is equal to mass x acceleration. In other words if a body has to move, there must be an external force. In this case athlete is moving. That means he is acted upon by an external force. That is in this case friction.
 
Remember friction always oppose the relative motion between two surface. Here athlete is trying to drag his feet against the ground in opposite direction of his movement. So the friction force acts in the opposite direction that is in the direction of his movement.
 
Hope this answer helps. Please do give me feedback on my answer. Thanks.
one month ago
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