A car travels at an initial velocity of 6.0 m/s and decelerates at –4.0 m/s2. How much time until?

In physics you look at units to organize your math. Velocity is 6m/s so you have to multiply by s to get a position.

p = t x v with t in seconds.

Then you have a in m/s^2 so

v(i) = v(0) + t x a and now you recompute the position using the sum of velocities.

p = t x (v(0) + t x a) Now plug in the given values and crank out an answer.

4.0m = t x 6.0m/s + t^2 x (-4.0 m/s^2)

4 = 6t - 4t^2

-4t^2 + 6t - 4 = 0 Quadratic formula time.

Negative b is the place to start,
Plus or minus will show you're smart,
The radical sits so gent-i-ly,
On b square minus 4ac
Now we're done ... except to say,
The whole thing sits on top of 2a