To save fuel, some truck drivers try to maintain a constant speed when possible.
ID: 1695843 • Letter: T
Question
To save fuel, some truck drivers try to maintain a constant speed when possible. A truck traveling at 28.0 km/hr approaches a car stopped at the red light. When the truck is 165.5 meters from the car the light turns green and the car immediately begins to accelerate at 2.4 m/s2. How close does the truck come to the car assuming the truck does not slow down?How far from the stop light has the car travelled when the truck reaches its closest distance?
( ps. i can not solve it the way i thought about because i do not have the final speed of the car ! )
Explanation / Answer
Once the car has reached 28 km/h it will be safe so the final speed of the car is 28 km/h because before that the truck is getting closer and closer, at 28 km/h the truck neither gets closer or further, and after 28 km/h the car gets further away. 28 km/h= 7.78 m/s. 7.78/2.4= 3.24 s the car will reach 28 km/h after just 3.24 s and at that point the truck will be the closest it will ever get. in that time the car averaged 3.89 m/s and the truck averaged 7.78 m/s so 3.89 m/s*3.24 s= 12.6036 m 7.78m/s*3.24s= 25.2072 m so the differnce between the 2 is 12.6 m 165.5-12.6= 152.9 m is the clostest the truck gets to the car, and he reaches this when the car is 12.6 m from the light. a. 152.9 m b. 12.6 m from the light
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