Question

A car is traveling at 20.0 m/s, and the driver sees a traffic light
turn red. After 0.530 s (the reaction time), the driver applies the brakes,
and the car decelerates at 7.00 m/s2. What is the stopping distance of the
car, as measured from the point where the driver first sees the red light?

Answer 1

d=vt+1/2at^2
t= 0.530 s
v=20.0 m/s
a=7.00 m/s2
solve for d

Answer 2

Yes I tried this but the answer in the back of the book is 39.2m
I get 9.62m.

Answer 3

his reaction time is .53 seconds, meaning
for .53 seconds, he's still travelling at 20 m/s

now after .53 seconds, he starts to decelerate

20-7t=0
solve for t, this is the amount of time in order to reach 0 velocity or in other words, to stop

then plug that into the distance

x=1/2 (-7)t^2+20t+x0

x0 is the same as the distance travelled during the reaction time (.53*20)

Answer 4

for 0.53 sec car travels with 20m/s--->distance covered = 10.6 m
now
since it decelerates, a=-7
u=initial vel = 20, v =0(car stops)
v^2=u^2+2as
0=400-2*7*s
s=28.57
total distance = 10.6+28.57 = 39.17m

Answer 5

first calculate the distance car travels during response time
D1 = speed * time
after that it de-accelerate by 7m/s^2
v^2 - u^2 = 2a*D2
put the values of v,u,a
net distance is D1 + D2

Answer 6

thank you ALL for your help

Answer 7

welcome :)
good question.