# A locomotive is accelerating at 2.33m/s2. It passes through a 20.0m wide crossing in a time of 2.00s. After the locomotive leaves the crossing, how much time is required until its speed reaches 40.0m/s?

## Expert Answers

Here in the equation

`s =v_0*t +(a*t^2)/2`

`V_0` is the initial speed (not the final speed after all the space s has been travelled). Therefore `V_0=7.67 m/s` is the speed at the beginning of the crossing.

The total time since the speed is 7.67 m/s until it is 40 m/s is of course `t=13.875 seconds` , but from this time one needs to subtract 2 seconds (the time that the locomotive needs to pass through the crossing).

The answer is `t =13.875-2 =11.875 seconds`

Approved by eNotes Editorial Team

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