Physics
posted by Anonymous .
A car moving initially at a speed of 80 km/h and weighing 13,000 N is brought to a stop ina distance of 61 m. Find(a) the braking force and (b) the time required to stop. Assuming the same braking force, find (c) the distance and (d) the time required to stop if the car were going 40 km/hr initially.

Vi = 80 km/ h * 1000/3600 = speed in m/s
find that
average speed during stop if deacceleration is constant = Vi/2
find that
time to stop = 61/(Vi/2)
find that  call it t
acceleration a = =  Vi/t
so
Force = m a =  m Vi/t

for Vi = (1/2) original Vi
then use F , same mass so same a
0 = new Vi + a t
that gives you new t
d = Vi t +(1/2) a t^2
or just use average velocity of Vi/2 and t 
a)5368 N
b)5.5 s
c)15.24 m
d) 2.74 s
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