Question

Exercises gives the positions s = f(t) of a body moving on a coordinate line, with s in meters and t in seconds.

Answer 1

Hi there!

a. Find the displacement by plugging in the values of the interval:

f(2) - f(0) = 0 - 2 = -2 meters.

Average velocity is the slope, thus:

$v_{avg} = \frac{f(2) - f(0)}{2 - 0} = \frac{0 - 2}{2 - 0} = -1$

The average velocity for the interval is -1 m/s.

b. To find the speed at the endpoints, we must take the derivative to get the velocity equation:

f(t) = t² - 3t +2

f'(t) = 2t - 3, at t = 0, speed = |-3| = 3 m/s. At t = 2, speed = 2(2) - 3 = 1 m/s.

Acceleration is the second derivative, thus:

f''(t) = 2. The acceleration is 2 m/s² for both endpoints.

c. When the body changes direction, the first derivative changes signs. Thus:

0 = 2t - 3

3 = 2t, t = 1.5 sec. This is where the body changes direction.