Answer
The car's velocity at t = 0 was 21 m/s
Work Step by Step
Let $v_1$ be the velocity at t = 4.0 s. We can use the 1.0-second time interval from t = 4.0 s to t = 5.0 s to find $v_1$. Therefore;
$\Delta y = v_1~t+\frac{1}{2}at^2$
$30~m = v_1(1.0~s)+\frac{1}{2}(2.0~m/s^2)(1.0~s)^2$
$v_1 = 29~m/s$
We can find $v_0$:
$v_0 = v_1-at$
$v_0 = 29~m/s-(2.0~m/s^2)(4.0~s)$
$v_0 = 21~m/s$
The car's velocity at t = 0 was 21 m/s.
