# A car traveling at 40 m/s must come to a stop in 120 meters What (constant) acceleration required how much time would pass while the car is coming to a stop?

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We can use the Equations of motion here.

`V^2 = U^2+2aS`

`V = 0` since the car comes to rest

`U = 40m/s`

`a = ???`

`S = 120m`

`a = (V^2-U^2)/(2S)`

`a = (0-40^2)/(2xx120)`

`a = -6.667m/s^2`

Using V = U+at

`0 = 40-6.667xxt`

`t = 6`

*So the constant deceleration is 6.667 and the time required to stop is 6s.*

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