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Let this function be x = 6t2 + 2t + 4

What is this object's acceleration?

I tried inputting 6, but it counted it wrong.

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"Stopping distance" is defined as the distance a car travels between the instant a driver sees a need for emergency stop and the instant that a car comes to rest when the brakes are fully applied. When an obstacle is first seen by a driver, the driver takes a certain time to react (traveling the "thinking distance") before applying the brakes. Then, the car must decelerate to a stop while the brakes are fully applied (traveling the "braking distance").

Consider a driver traveling with a speed of 40 m/s. A child runs out into the roadway in front of the driver, and the driver takes 0.7 seconds to react to this need to suddenly stop. The brakes provide a constant deceleration rate of -10 m/s2. How far does the car travel before coming completely to rest?

A full explanation on this question would be extremely helpful, thanks.

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A car traveling to the right with initial speed 28 m/s must come completely to rest over a distance of 49 meters in order to pass a brake test. What acceleration must the car have? (Let the rightward direction be considered positive.)

I'm confused on what equation I should use to answer this one/

__Equations__:

v= v(naught) + at

x = x(naught) + v(naught)t + (1/2)at^2

v^2 = v(naught)^2 + 2a (x-x(naught))

**Thank You,**