Use the following to answer questions :
A driver going down a straight highway is traveling at 70 ft/sec on cruise control when he begins accelerating at a rate of 4.2 ft/sec 2 . The final velocity of the car is given by the function , where V(t) is the velocity at time t.
-If the car is traveling at 100 ft/sec, for how long did it accelerate? (Round to the nearest tenth of a second.)
A) 6.9 seconds
B) 7.1 seconds
C) 7.3 seconds
D) 7.5 seconds

Question

Use the following to answer questions :
A driver going down a straight highway is traveling at 70 ft/sec on cruise control when he begins accelerating at a rate of 4.2 ft/sec 2 . The final velocity of the car is given by the function  , where V(t) is the velocity at time t.
-If the car is traveling at 100 ft/sec, for how long did it accelerate? (Round to the nearest tenth of a second.)
A) 6.9 seconds 
B) 7.1 seconds 
C) 7.3 seconds 
D) 7.5 seconds

Quizplus · Accepted Answer

We need to solve for the time t when V(t) = 100 ft/sec.

100 = 70 + ∫4.2 dt from 0 to t

100 = 70 + 4.2t

30 = 4.2t

t ≈ 7.1 seconds (rounded to the nearest tenth)

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