a car a moving at rate of 72km/h and applies brakes which provide a retardation of 5ms-2 how much time does the car takes to stop
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Initial velocity of the car=72km/h=72*5/18=20m/s
retardation= 5m/s2
therefore accelaration = -5m/s2
Final velocity=0
(i)Time taken=?
we know,a=v-u/t
=> -5=0-20/t
=> -5=-20/t
=> -5t=-20
=> t = -20/-5=4sec
(ii)s=ut=1/2at2
=> s=20*4+1/2*-5*42
=> s=80+1/2*-5*16
=> s=80-40=40m
(iii)if speed is doubled u=40m/s
s=ut=1/2at2
=> s=40*4+1/2*-5*42
=> s=160+1/2*-5*16
=> s=160-40=80m
retardation= 5m/s2
therefore accelaration = -5m/s2
Final velocity=0
(i)Time taken=?
we know,a=v-u/t
=> -5=0-20/t
=> -5=-20/t
=> -5t=-20
=> t = -20/-5=4sec
(ii)s=ut=1/2at2
=> s=20*4+1/2*-5*42
=> s=80+1/2*-5*16
=> s=80-40=40m
(iii)if speed is doubled u=40m/s
s=ut=1/2at2
=> s=40*4+1/2*-5*42
=> s=160+1/2*-5*16
=> s=160-40=80m
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