Mechanics question ( easy )?

  • Thread starter Thread starter Prankur M
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Prankur M

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If a car starts from rest with acc. 5 m/sec^2.Then remains constant for some time.Then decelarates at 5m/sec^2 and comes to rest.Total distance- 500 m total time 25 sec.Find time the car stayed in constant velocity
 
d1=.5*5*t1^2
d2=5*t1*t2
d3=5*t1*t3-.5*5*t3^2
d1+d2+d3=500
t1+t2+t3=25

solve for t2
.5*5*t1^2+5*t1*t2+5*t1*t3-
.5*5*t3^2=500

t1+t2+t3=25

lools like 3 unknowns, however, since the acceleration was equal in magnitude for t1 and t3, and the average speed was the same for both, t1=t3

.5*5*t1^2+5*t1*t2+.5*5*t1^2=500
2*t1+t2=25
t1=(25-t2)/2

t2=sqrt(25^2-400)

15 seconds

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