Question

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 5.2 m/s2 for 4.5 seconds. it then continues at a constant speed for 13.4 seconds, before applying the brakes such that the car's speed decreases uniformly coming to rest 437.29 meters from where it started. the yellow car accelerates uniformly for the entire distance, finally catching the blue car just as the blue car comes to a stop. 1) how fast is the blue car going 3.6 seconds after it starts?

Answer 1

19 m/s
This is an exercise in ignoring unneeded data. We want to know how fast the blue car is going after 3.6 seconds. The acceleration is 5.2 m/s^2 for 4.5 seconds. Since 4.5 is greater than 3.6, we know the car was under constant acceleration of 5.2 m/s^2 for the entire 3.6 seconds. So we just need to multiply to get the answer. 3.6 s * 5.2 m/s^2 = 18.72 m/s
Since we only have 2 significant figures in our data, we need to round to 2 significant digits, giving 19 m/s