Answer:
7.5 seconds
Explanation:
We can use the second equation of accelerated motion
vf = vi + a Δt
We know that the intial velocity (vi) is 30m/s, and the final velocity is 0 since it comes to a stop. We also know that the acceleration is -4m/s.
We can rearrange the equation for Δt (time)
vf = vi + a Δt
vf - vi = a Δt
(vf - vi)/a = Δt
and we can substitute the values into the equation for Δt now
Δt = (vf - vi)/a
Δt = (0 - 30)/-4
Δt = -30/-4
Δt = 7.5
