1. David is driving a steady 29.0 m/s when he passes Tina, who is sitting in her
ID: 1572722 • Letter: 1
Question
1. David is driving a steady 29.0 m/s when he passes Tina, who is sitting in her car at rest. Tina begins to accelerate at a steady 2.70 m/s2 at the instant when David passes.
A) How far does Tina drive before passing David?
B) What is her speed as she passes him?
2. You are driving to the grocery store at 16 m/s. You are 160 m from an intersection when the traffic light turns red. Assume that your reaction time is 0.50 s and that your car brakes with constant acceleration.
A) What magnitude braking acceleration will bring you to a stop exactly at the intersection?
Explanation / Answer
1 )
a )
using s = u t + 1/2 a t2
0 = 29 t - 0.5 X 2.7 X t2
1.35 t = 29
t = 21.48 sec
the distance is of Tina is 21.48 X 29 = 622.92 m
b )
velocity of Tina
v = 21.48 X 2.7
v = 57.996 m/s
2 )
A )
d = v t = 16 X 0.5 = 8 m/s
s = 160 - 8 = 152 m/s
using v2 - u2 = 2 a s
a = ( v2 - u2 ) / 2 s
a = 0 - 162 / 2 X 152
a = - 0.842 m/s2
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