Two cars start from rest at a red stop light. When the light turns green, both cars accelerate forward. The blue car accelerates uniformly at a rate of 5.3 m/s2 for 4.7 seconds. It then continues at a constant speed for 14.3 seconds, before applying the brakes such that the car
1 )
Data for blue car ::
initial velocity of blue car = Vbi = 0 m/s
acceleration of blue car = ab = 5.3 m/s2
time of travel = t = 1.9 sec
using the kinematics equation ::
Vf = Vi + at
Vf = 0 + (5.3 m/s2 ) (1.9 sec)
Vf = 10.07 m/s
2)
initial velocity of blue car = Vbi = 0 m/s
acceleration of blue car = ab = 5.3 m/s2
time of travel = t = 8.7 sec
using the kinematics equation ::
Vbf = Vbi + abt
Vf = 0 + (5.3 m/s2 ) (8.7 sec)
Vbf = 46.11 m/s
3) Velocity of blue car after 4.7 sec can be given using the equation
Vbf = Vbi + abt
Vbf = 0 + (5.3 m/s2 ) (4.7 sec)
Vbf = 24.91 m/s
Distance travelled in 4.7 sec can be calculated using ::
d = Vbi t + (0.5) ab t2
d = 0 x 4.7 + (0.5) (5.3 m/s2 ) (4.7 sec)2
d = 58.54 m
distance travelled in 14.3 sec at constant velocity of 24.91 m/s :::
d' = (24.91 m/s) (14.3 sec) = 356.2 m
d' = 356.2 m
Total distance travelled by blue car before applying the brakes
d + d' = 58.54 m + 356.2 = 414.74 m
4) total distance covered by the blue car = 444.02 m
total distance covered by the blue car before applying brakes = 414.74 m
distance covered by blue car after applying brakes = D = 444.02 - 414.74 = 29.28 m
D = 29.28 m
initial velocity before applying brakes = Vi = 24.91 m/s
final velocity = Vf =0 (since the car stops)
Using the kinematics equation ::
Vf2 = Vi2 + 2 a D
02 = 24.912 + 2 a (29.28)
a = -10.6 m/s2
5) time for acceleration = 4.7 sec
time for constant velocity = 14.3 sec
time for retardation can be calculated using the equation ::
Vf = Vi + at
0 = 4.91 m/s + (-10.6 m/s2 ) t
t = 0.463 sec
So total time of travel = 4.7 sec + 14.3 sec + 0.436 sec = 19.436 sec
6 ) distance travelled by yellow car = d = 444.02 m
initial velocity = Vi =0
time of travel= 19.436 sec
using the equation ::
d = Vi t + 1/2 a t2
444.02 = 0 t + (0.5) a (19.436)2
a = 2.35 m/s2
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