Question

a car travels at uniform velocity of 20m/s for 5 seconds, the breaks are then applied and the car comes to rest with uniform retardation in further 8 seconds. draw a graph of velocity against time.How far does the car travel after the breaks are applied.?
They are brakes.

after 5 sec at constant v
Vi = 20
v = 20 + a t where t is total time - 5
v = 0 when t = 8 so
0 = 20 + a (8)
a = -20/8 = - 5/2
so
v = 20 - (5/2) t = 20 - (5/2)(time - 5)
68.75m
They are brakes.

after 5 sec at constant v
Vi = 20
v = 20 + a t where t is total time - 5
v = 0 when t = 8 so
0 = 20 + a (8)
a = -20/8 = - 5/2
so
v = 20 - (5/2) t = 20 - (5/2)(time - 5)

physics - Anonymous, Tuesday, June 16, 2015 at 4:02am
68.75m
Slope=AB÷OB
=20m/s÷5s
=4m
-acceleration=retardation
-4m

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