Question

A person driving her car at 12.5 m/s approaches an intersection just as the traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before turning red, and she is 28 m away from the beginning of the intersection, which is 15 m wide, as shown below. Using the gas pedal she can accelerate at 3.5 m/s2 and using the brake pedal she can accelerate at –5.8 m/s2. Ignoring reaction time and car length, determine whether she should try to stop or speed up to be a legal driver.

Answer 1

She should try to stop the car.

We will discuss the possibilities of trying to stop and trying to speed up in 2s and find the distance she travels to get into a conclusion.

If she try to stop, then the acceleration, a = -5.8 m/s²

Initial velocity, v₀ = 12.5 m/s

Final velocity, v₁ = 0 m/s   [Since the car is stopped]

Let d be the distance the car travels before stopping.

Then, we have, v₁² = v₀² + 2ad

Therefore, d = v₁²-v₀²/2a

                     =  0-(12.5)²/2 x (-5.8)

                     = 156.25/11.6

                     = 13.47 m

So she can stop in time as she is 28m far from the beginning of the intersection.

If she try to speed up, then the acceleration of the car, a = 3.5 m/s²

Initial velocity of the car, v₀ = 12.5 m/s

Time she have, t = 2 s

Let d be the distance the car travels in 2 s.

Then, d = v₀t +(1/2)at²

            = 12.5 x 2 + (1/2) x 3.5 x 2²

            = 25 + 7

            = 32 m

She is 28 m before the beginning of the intersection which is 15 m wide. So if she speed up she will be in the middle of the intersection when the light turns red and may have to stop.

Hence as a legal driver, she should try to stop the car.

Learn more about acceleration at brainly.com/question/605631

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