Starting from rest,a car accelerates at a rate of +4 m/s² for 3 seconds.The car then travels at a constant speed for 5 seconds.What is the displacement of the car after moving for a total of 8 seconds? A)32 m B)36 m C)72 m D)78 m E)128 m

Question

Quizplus · Accepted Answer

Using the formula for displacement with constant acceleration: 
s = ut + 1/2at^2 
s1 = 0 + 1/2(4)(3)^2 = 18 m 
After the first 3 seconds, the car is traveling at a constant speed for 5 seconds, so its acceleration is 0. 
Using the formula for displacement with constant velocity: 
s = vt 
s2 = 4 m/s * 5 s = 20 m 
The total displacement is the sum of s1 and s2: 
stotal = s1 + s2 = 18 m + 20 m = 38 m 
Therefore, the correct answer is D) 78 m.

Starting from Rest,a Car Accelerates at a Rate of +4