OG详解-OG1 数学2 Q4

Choice D is correct. In the given equation, s  is the speed, in miles per hour, of a certain car t seconds after it began to accelerate. Therefore, the speed of the car, in miles per hour, 5 seconds after it began to accelerate can be found by substituting 5 for t  in the given equation, which yields s = 40 + 3(5), or s = 55.    Thus,the speed of the car 5 seconds after it began to accelerate is 55 miles per hour.
Choice A is incorrect and may result from conceptual or calculation errors.
Choice B is incorrect and may result from conceptual or calculation errors.
Choice C is incorrect and may result from conceptual or calculation errors.