plzzz help..?

Question

A skater moving at 5m/s begins to decelerate at 2m/s each second. How fast will it be moving after 4 seconds.
show me how you did it. tnx

Answer 1

The relation between speed, acceleration, and time is:

v = v0 + at where a = acceleration, t = time and v0 = speed at the start of the acceleration.

Now you are told that the skater decelerates 2 m/s every second so the acceleration is

a = -2 m/s/s = 2 m/s^2 The "-" sign indicates the skater is slowing down.

The skater starts at a speed 5 m/s so plugging in to the above equation:

v = v0 + at = 5 m/s + (-2 m/s^2)*(4 s) = 5 m/s - 8m/s = - 3 m/s

The minus sign means the skater is now moving in theopposite direction from her original direction.

Answer 2

okay, we use the equation a=(vf-vi)/t

we know a = -2 (minus sign because we're deccelerating)
we know vi=5
we know t=4

plug all these into the equation: -2=(vf-5)/4
-8 = vf-5
-3 = vf

so our final velocity is -3 m/s